I have seen that a bit with simple posts a couple of times lately.
If you start a post, then get interrupted and come back to it later, it can fail.
Going to first unread and starting over fixes it.
I have also have the problem and reported it to the webmaster (@denzil). For me the problem is sporadic, this seems to happen when an auto-save or manual save of a draft occurs and also sometimes when replying to a thread. Tapatalk never seems to have issues for me.
