Unexplained/unpredictable font substitutions

I do a lot of work with animated type in Motion, and I’ve occasionally encountered a type glitch that today is driving me up the wall.

Every time I open a Motion file, make any kind of an edit, and export it to a QuickTime file, it’s a better than even chance that Motion will change the font of something that I didn’t even touch. The type usually stays within the same family (such as: changed from heavy to extra light oblique), although a few times it has actually replaced a font with a completely different typeface that’s used elsewhere in the same Motion project. So far, it hasn’t swapped a typeface for one that’s not used somewhere in the Motion file, however.

What’s stranger still is that this glitch shows up in different ways. After I’ve exported the animation and notice an error (say something that’s supposed to be heavy has been rendered as extra light oblique), I’ll go back into Motion, and sometimes the font properties will have been changed in the inspector (the inspector now says extra light oblique), even though I never changed it or even touched that particular text block in any way. Other times, the inspector doesn’t show the incorrect font—so in other words, it was heavy in the inspector and the player before the export, it shows up as heavy in the inspector and player after the export, but somehow (inexplicably) the export itself came out as extra light oblique.

Font Book doesn’t show any issues with the typefaces in question, and relaunching Motion, restarting my Mac, trashing prefs (etc.) don’t seem to have an effect. I’ve exported this same file probably ten times or more today, and each time, something different has been altered.

Has anyone else experienced similar issues or know of risk factors that might contribute to this type of rendering error?