Thank you Charles, for your response. After I posted, I stumbled upon a thread on a Microsoft site, where an author had the same complaint. An "expert" admitted the issue and explained that there's no way to change it. When the author pointed out that the problem didn't exist on 2003's version, the conversation stopped.

Apparently, the only way to "fix" the issue is to stop spell check from running in specific blocks of texts (a pain if you're dealing with hundreds of pages).

It's a shame they can't fix something so glaringly obvious.