Hold down Alt and Control Keys while choosing your font ( This works on Windows )
Thanks so much!!
FYI: We had a similar font problem today, where FileMaker Pro wouldn't let us change the font on a field. Every time we changed the field to our desired font (Myriad Pro), it snapped back to the default font (which happened to be Helvetica).
At first, we thought it was a FileMaker Pro issue, but then we realized that it was actually a font conflict on our Mac.
We went into the Mac's Font Book utility and found multiple duplicates of the Myriad Pro font. In Font Book, we simply clicked on the "Resolve Automatically" button to disable all the duplicate fonts, and everything started working again in FileMaker Pro... as soon as we quit & relaunched FileMaker Pro.
Just posting this here in case it helps anybody else in the future!