I observed this behavior again yesterday evening (Eastern Time US), and was able to experiment with it a little bit:
- The list of comments on three threads (all the threads that I checked) was incomplete, in that a complete list of comments was not presented.
- The appearance of the page was entirely correct, although its display of the thread content was stale.
- Emptying the browser cache did not change the result.
- Examining the page on another browser also did not change the result: it was stale there, too, and identically so.
- Upon logging-in, the content of the threads was now current. Additional comments appeared which had not been there before.
- The other browser, which was not logged-in, continued(!) to display the stale content: the pages as displayed by the two browsers, one logged-in and the other not, was now different for these threads. (I only “refreshed” the page: I did not re-request the URL, nor did I think to flush the cache on the second browser. I do know that this browser is set to flush its cache on program startup and shutdown.)
Although this behavior is only an annoyance (along with the occasional “disappearing session,” which I somewhat suspect might be related), I offer this finding in hope that the gods might be able to find and fix it. (The last bullet-point makes me wonder if it really is or isn’t a problem with a down-stream caching server, and I unfortunately did not do an exhaustive test with the second browser when the opportunity to do so had presented itself.)