Hmm!
I'm trying to be more consistent about my browsing habits to see if I can find a pattern.
Maybe I used a "back-arrow" in a browser while reading a thread, instead of exiting normally.
I seldom paid attention to the distinction between visiting a forum and reading every thread.
I just know that relatively often I see "black dashes" above "red Yeses" in a forum's list of threads, and that seems as if it should be extremely infrequent.
Is there any chance that some parts of ATP could be sorting on "poster's local time" and other parts sorting on UT? I doubt it, but that's one thing that might let "old" East Coast posts sort "above" newer West Coast posts.
(I blamed IE 7 for months, but now I'm using FireFox. I still think the likeliest answer is "User Confusion".)