Okay! Very sorry for double-posting, but I discovered the source of the problem! It was the Minigames Collection mod, specifically, the bike chase model replacement option. Oddly, chocobo racing model replacement works fine, just not bike chase. It's not a huge deal, I can live without that, but I'll probably drop chocobo racing replacement as well just for consistency. xD
Thanks again to everybody for their help, glad we could sort this out. Is there anywhere I should post a bug report or something like that?