I've typed several posts over the last week (just happened again) which got 'lost' in the way you described when I tried to post them. A bit irritating when, as in one case, it was a detailed post on a technical VAT point.

Previously, I had found that the browser back button would take ma back to the posting screen but on these occasions I got a 'page expired' message when I tried that.

Seems like a server fault at YBW end?