Lord's Prayer in a Papyrus (Probable Amulet)

Brent Nongbri in “The Lord’s Prayer and XMΓ: Two Christian Papyrus Amulets,” The Harvard Theological Review, vol. 104, no. 1, 2011, pp. 59–68 (JSTOR), presented a papyrus tentatively dated to the 6th or 7th century.  The papyrus is thought to have been an amulet papyrus, something folded up and worn on the body of the person who owned it.  The text of the Lord's Prayer on the papyrus ends (as in other early witnesses) without the doxology familiar to KJV readers.  This is the opposite of what one's expectation would be if (1) this was intended as being worn for the purpose of having some kind of special power and (2) if the person who made it thought that the prayer included the doxology.  The best explanation seems to be that this early witnesses (identified as P.CtTBR inv. 4600 in the article) was created by someone who did not think that the doxology was a part of the Lord's Prayer.  Of course, it is not certain that this was an amulet (only "probably an amulet" according to the article).  The papyrus itself is not the best possible witness to the text of the Lord's Prayer for lots of reasons (there is some wear and tear, and poor spelling).  Nevertheless, if one holds that the doxology was originally part of the Lord's Prayer, this kind of document seems hard to explain.