This just happend to me twice in a row in the trade forum:

I used quick reply to reply to something, then after it was posted, I wanted to edit, so I used the Edit button.. after 1 push of the button, nothing happend, no page was loaded, no edit whatever, so I pushed the button again, and got a message that I was trying to reach an invalid page orso.. after that my reply was gone... thinking I accidentily pushed the remove button I used quickreply again to reply, and as I usually make typo's I wanted to edit again, and again same story, reply was gone, don't know if it will suddenly reappear in a while, and maybe show a dubble post then...
maybe it's just me messing up, or maybe it's a bug in the board, but I thought I'de mention it...