Most likely they borrowed one of the dancier tunes from the Cantigas de Santa Maria of Alfonso X and didn't remember (or ever know) what it was and how to spell it.

http://www.pbm.com/~lindahl/cantigas/

https://en.wikipedia.org/wiki/Cantigas_de_Santa_Maria

Practical modern performing edition (I have this):

http://www.gaita.co.uk/publications.html

A facsimile, for the REALLY serious mediaeval music buff:

http://imslp.org/wiki/Cantigas_de_Santa_Maria_%28Alfonso_X_of_Castile%29