I don't think it's a client-side problem.

Actually, it happened again and I figured out what was wrong. It was a client-side problem, but it was essentially PEBKAC error. Here's what I'd done:

- I like clearing cache and cookies frequently, so I'd enabled the MyIE2 feature to do so on each browser exit.

- But I hadn't exited the MyIE2 session, I was in the middle of a post. So I knew that the clear-on-browser-exit hadn't been the culprit.

- Actually, it turns out that it had been the culprit. I was browsing another site in a completely different session of MyIE2 (not just a different tab, but a whole separate window) and had closed that window.

Conclusion: MyIE2's feature to clear cache and cookies on exit applies to each instance of the program, not to all instances of the program globally. Wonder if they take feature requests...