1540: "In his conception all of Mary's flesh and blood was purified so that nothing sinful remained . . . Each seed was corrupt, except that of Mary."One of the other Roman Catholics there indicated that he thought these quotations were "worthy of consideration."
1544: "God has formed the soul and body of the Virgin Mary full of the Holy Spirit, so that she is without all sins."
1545: ". . . the pure Virgin Mary, who has not sinned and cannot sin for ever more."
With respect to the 1540 quotation, "his conception" refers to Jesus' conception, not Mary's. Mary's seed is Jesus. Joachim & Anna's seed was Mary. This quotation from 1540, therefore, stands opposed to the dogma of the IC.
Moreover, the reference to "purified" is a reference to the flesh that Jesus took from Mary. Again, that reference shows that Mary was not pure and consequently the flesh taken from her had to be purified. Had Mary been preserved from all taint of sin, she (i.e. her flesh) could not have been purified any more than one can remove inclusions from a flawless stone.
The context of the 1540 quotation can be found in this more complete translation:
Every man is corrupted by original sin and has concupiscence. Christ had neither concupiscence nor original sin. Therefore he is not a man: Response: I make a distinction with regard to the major premise. Every man is corrupted by original sin, with the exception of Christ. Every man who is not a divine Person [personaliter Deus], as is Christ, has concupiscence, but the man Christ has none, because he is a divine Person, and in conception the flesh and blood of Mary were entirely purged, so that nothing of sin remained. Therefore Isaiah says rightly, "There was no guile found in his mouth"; otherwise, every seed except for Mary's was corrupted.(source)
The context confirms what I explained above. This quotation teaches against the Immaculate Conception of Mary, and affirms only the immaculate conception of Christ.
As for the 1545 quotation, here is the context:
The Most Hellish Father, St. Paul III, in his supposed capacity as the bishop of the Roman church, has written two briefs to Charles V, our lord emperor, wherein he appears almost furious, growling and boasting, according to the example of his predecessors, that neither an emperor nor anyone else has the right to convoke a council, even a national one, except solely the pope; he alone has the power to institute, ordain, and create everything which is to be believed and done in the church. He has also issued a papal bull (if one may speak like that) for about the fifth time; now the council is once again to take place in Trent, but with the condition that no one attend except his own scum, the Epicureans and those agreeable to him—whereupon I felt a great desire to reply, with God’s grace and aid. Amen!(LW 41:263-264) (source)
First, I beg you, for God’s sake, whoever you are, a Christian, indeed, even if you still have natural reason, tell me whether you can understand or comprehend what kind of a council that would be, or whether it could be a council, if that abominable abomination in Rome, who calls himself pope, has such reservation, power, and authority to tear up, change, and ruin everything that is decided in the council, as most of his decrees bellow. Doesn’t it seem to you, my dear brother in Christ, or my dear natural-reason friend, that such a council would have to be nothing but a farce, a carnival act put on to amuse the pope.
What is the use of spending such great pains and effort on a council if the pope has decided beforehand that anything done in the council should be subjected to him, that nothing should be done unless it pleased him very much, and that he wants the power to condemn everything? To avoid all this trouble it would be better to say, “Most Hellish Father, since it makes no difference at all what is or will be decided before or in or after the council, we would rather (without any council) believe in and worship Your Hellishness. Just tell us beforehand what we must do; “Good Teacher, what shall I do?” [ Mark 10:17 ]. Then we shall sing the glad hymn to Your Hellishness, “Virgin before, in, and after childbearing,” since you are the pure Virgin Mary, who has not sinned and cannot sin for ever more. If not, then tell us, for God’s sake, what need or use there is in councils, since Your Hellishness has such great power over them that they are to be nothing, if it does not please Your Hellishness. Or prove to us poor, obedient “simple Christians” whence Your Hellishness has such power. Where are the seals and letters from your superior that grant such things to you? Where is written evidence which will make us believe this? Won’t Your Hellishness show us these things? Well then, we shall diligently search for them ourselves, and with God’s help we shall certainly find them shortly
As you can see, the comment is one that is made in the midst of a rhetorical and sarcastic comment directed at the pope. Luther isn't necessarily setting out his own view of Mary any more than he is trying to analyze the pope's view of her. He's simply trying to mock the pope.
And, of course, the conception of Mary isn't in view at all. In other words, even if we assumed that Luther was describing his own view of Mary, it would only describe her sinlessness, not her immaculate conception.
Again, we see that the Romanist who brought this quotation was taking the comment out of context and distorting its meaning.
The "1544" quotation was a little harder to track down. There's a reason: the Romanist has given us the wrong year.
The item that the Romanist is citing is this: "God has formed the soul and body of the Virgin Mary full of the Holy Spirit, so that she is without all sins, for she has conceived and borne the Lord Jesus." for which the citation given by Thomas O'Meara, who seems to have introduced this translation, is (WA 52, 39).
That citation is actually to a sermon from 1532. Although WA 52 is titled "Hauspostille 1544," that is Luther's "House Postils" published in 1544, but containing mostly sermons from the first half of the 1530's. Luther did assent to having the sermons published, but the work was earlier work. Specifically, Veit Dietrich published these sermons based on Veit Dietrich's sermon notes, with Luther's assent (see discussion here). This particular sermon was apparently first publicly preached in 1532 and then again in 1533, according to the index in WA 52.
The German context for the quotation is this:
An English translation of the entire sermon has been provided by Rev. D. M. Martens.
The context provided above is translated in English as follows:
Adam and Eve were not born, but created. God made Adam out of the dust of the earth, and the woman of his rib. How much nearer is Christ to us than Eve to her husband Adam, since He is truly our flesh and blood. Such honor we should highly esteem and well take to heart, that the Son of God became flesh, and that there is no difference at all between His and our flesh, only that His flesh is without sin. For He was so conceived of the Holy Ghost, and God poured out so richly His Holy Spirit into the soul and body of the Virgin Mary that without any sin she conceived and bore our Lord Jesus. Aside from this, in all other respects, He was like other men; He ate, drank, was hungry, thirsty, cold like other men. Such and similar natural infirmities, which have descended upon us by reason of sin, He, who was without sin, bore and had like unto us, as St. Paul says: "He was made in the likeness of men, and found in fashion as a man."(source)
As can be seen from the context, the issue is Jesus' conception, not Mary's. She conceived and bore Jesus without sin. It is a reference to his immaculate conception, not hers.
UPDATE: I had drafted the above and then let it sit so that I could come back to it and proofread before posting. Meanwhile, I see that James Swan has, essentially independently, provided some similar comments to my own as to the third item above. This is reassuring to me, since Mr. Swan is a great resource for this sort of question about Luther.