Yes, I've found the same thing, though as Les says, it's intermittent.

Also, sometimes when I click Submit - with the preview box NOT ticked, so the message should then appear on the boards - it can just disappear without a trace or visible effect. A number of brilliant pearls of wisdom have been lost to civilisation that way. Now I scribble my sacred utterances down on Wordpad or TextEdit before sending them on their way, and sometimes I need to go back and copy-paste them again: it usually works on the second try, though once it took about four attempts. (Maybe the fates were trying to tell me something?)

I use both Windows-XP-Firefox, and Apple-OSX-Safari&Firefox. I think it has happened with both machines but can't be sure. It definitely happens with Windows.