I get that problem from time to time myself. Emptying cache and reloading solves it.
But I have another problem I wanted to report. I tried to upload a bit of a longer text with a couple of formatting in it, putting some of it in italics using the usual. It didn't work. Since I had also a picture attached with the post, I thought at first that might be the problem, but it wasn't. Using a different one and even posting without any gave me the same error back. When I posted without the formatting it went through like a charm. But the text got less readable this way. Or different to what I intended. So there seems to be a problem with multiple formattenings within one text. At least on firefox and for me.