Excel 2007: Screenupdating=false triggering randomly

Well, I think it happened again. I tried checking whether screenupdating was disabled using the offered code, and Excel announced that screenupdating was, in fact, enabled. The odd thing was that immediately, control of the file was reestablished as well, so that it didn't act disabled any more.

Theories:
-I was imagining it this time and it didn't have a problem, so screenupdating was enabled the whole time (unlikely).

-I wasn't imagining things, but the problem isn't screenupdating, but something else that happened to resolve itself at the same time I asked for the status of screenupdating, which reported enabled because it was enabled the whole time (probably unlikely because specifically reenabling screenupdating has fixed the problem, at least temporarily).

-Accessing the flag to determine the status of screenupdating nudged Excel enough to knock it out of whatever problem it was having and caused screenupdating to become enabled again (likely, but inexplicable). This also implies that screenupdating is a symptom of something else gone wrong, not the problem itself.

Thoughts?

By the way, I think cells going blank is a different problem. I get some or all of the displayed rows of data in a file going blank almost every day, particularly files where I have relatively large tables (more than 100 rows of data) and scroll back and forth within the table a lot. Highlighting those rows or paging back and forth restores visibility without a problem. In that case, the file is never unresponsive and doesn't lose any data; it's simply forgetful of what data it's supposed to be displaying for some reason. My theory on that is that there's a memory leak somewhere.