Okay, I THINK I've tracked down the issue. It was actually a problem with the RSS feed running in one of our left-side islands. I turned off all the feeds, and as I turned them on one at a time, this particular one threw off the screen formatting each time it was turned on.
So, it looks like a problem with the feed from the destination site, rather than a problem with our site coding.
Thanks, guys! I'll follow up here if the problem recurs and my guess proves to be wrong. :-)
