Just had the same error as this afternoon, everything was Ok then I read a thread and the quote box was already open, tried to collapse and it wouldn't, went to a different theme based on bulletin default and it worked OK but the one I usually use is heavily customised, no idea why it does it a random though
More on this, it happens only in certain threads and only where there is more than one quoted box, the first quote works fine and collapses or opens, the second and subsequent are open when the page loads , if you try and collapse them it opens or closes the quote in the earliest post, weird.