It's almost as though sometimes it is honoring timezone, and other times not.
I once saw that where one db access was started up under csh with no TZ (so defaulted to midwest), while others were pst korn shell. People accumulating time data from east and west coasts were going nuts.
Could it be that the system is simply showing the local time of the user? Which is however irrelevant in terms of the order postings come in?
If I had designed the forum system I would not rely on time, but rather use a system generated sequential ID when people are transmitting their stories, similar to Oracle SCN.