Thank you for posting.
You are correct, if you have corruption of fonts in the FontBook, there can be problems displaying them.
Please try to add a few new fields to this layout, and select a true-type font -- Helvetica, for instance -- for these fields. If these do appear, but your other fonts do not, the next step to take is to fix those problem fonts in FontBook.
Let me know if you need clarification on this.
Thanks for your reply. I posted a similar description on Apple Support forums, and the answer that worked was to trash the filemaker cache.