Mind you this is on an iPhone...all those "technical" stuff is hidden from the end user
It could very well be a client issue...but I have only ever experienced it here. So, forgive my bluntness, but i'm not too impressed with phpbb and their dev's after discovering their attitude towards the image rotation issue
What I did notice when previewing/posting to that client was that someone else posted to the same thread while I was previewing/posting my response. And that response is there...mine is not. I have also noticed that at least one of my "replies" to my Polymax thread is lost-in-space

I knew I had replied...but a few days later when I checked back it was not there.
I just wanted to post my experience for reference...this is probably just as tricky as the "logout issue" I, and in that case, others have seen. Something that still happens...but not as frequently as before.