it happens to me as well just as john walker described. it's really annoying. but i thought it was the same for everyone, so when Ian Giles does them long posts, i scratched my head in wonderment! cos i have to try and say what i'm gonna say before the box gets full. BTW i'm using I.E 8 and xp?
i've got chrome but fell out with it, i'll try it again.
i wont have anything to say now 
I've got one PC running on Windows Vista with IE8 and an old PC on XP and Mozilla Firefox and the problem (post replies moving) started a few weeks ago on both PC's at the same time, so I think it's this site.