It's been weeks, so I don't think it is cache. But I'll try manually clearing it. I know that I do see it when I switch to the IE mode (I'm using Firefox). I have three computers, and I know it doesn't happen on one of the three. (I don't know about the other of the three.)
Yup, it was the cache! It needed a manual clearing... not sure why it didn't just cycle its way through... maybe I just don't use this computer enough... or maybe the cache it too big!
Interesting.... so my browser basically asked for that resource, and was given an empty file (which is valid for .gif), and just would continue to use that until it ran out of room to hold onto it... I don't really know how these caches work, but perhaps the fact that that image is practically on every page on the website, its place in the cache gets refreshed every day.