Hi! Thanks for doing that!
I've just checked, and the results are a bit puzzling.
From my laptop (which, incidentally, is where I did all the image editing and from which I uploaded the images), the behavior has not changed. I just checked both before and after a reboot. That was with Chrome. And the laptop is running Windows 7.
Post-reboot, I've now also checked using IE9 and Firefox 17.0.1. Same behavior.
I checked with Firefox on another Windows 7 computer also, a computer that hadn't yet visited my site. Same thing as originally reported.
I've also rebooted my tablet, an HP Touchpad running webOS v3.05, which uses a webkit-based browser. No change from last night, even after rebooting that as well.
On the plus side, when I checked with my iPhone 4S (Safari), without having rebooted it, I saw it initially load the implicated pages with the old image, but, without refreshing the page, I noted that the browser switched to the new image--either just after it finished loading the page or very close to the end of the loading.
So there's a positive indication...though the rest of them seem unchanged...
This is about 7 hours after your post.
I expect that I could just avoid this problem altogether by re-naming the new image and uploading that, replacing the images in my pages with that newly renamed image, but I would kind of like to understand what's going on here, or at least how to prevent the problem...I usually like the filenames that I use...