No, it's not a bug - it was a licensing restriction (exactly as the Adobe error message said), which the newer version of the font doesn't have. New fonts can (and sometimes do) have similar licensing restrictions.

I'm glad you got the problem sorted, but from all you've said it seems you still might not have removed the offending WP MathA font from the document.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]