Yet another decade-old thread turning up that is interesting and new to me.

As for the theory mentioned in the OP, I am not convinced. The fourth note said to have been erased is a) not visible at all, and b) harmonically wrong, inconsistent with the rest of the song. Thus the entire idea collapses.

In fact an antagonism between Christian and secular poetry is not typical for the 13th century. Distinction, yes, but the authors and composers very often covered both fields, and so did the audience.