I have had a couple "lost posts" similiar to what you describe. I'm pretty sure that this is what happened to mine...
When you initially type in your post and hit "continue" the screen advances to a preview mode which displays your post twice...the top screen is the preview screen and the bottom screen is the edit screen. Both of the screens have a "Continue" button. If you press the top "continue" button it submits your post. If you press the bottom "continue" button it'll merely update the two screens and leave you at the preview screen without having submitted the post. I have pressed the bottom "continue" button and then exited out of the post screen thinking that I have submitted the post when I hadn't.
After submitting a post I have a habit of going back to the discussion page and updating (refreshing) the screen by selecting one of the "Last hour/12 hours/24 hours" buttons to see if my post is displayed. That is when I find out that my post did or did not get submitted.
Muhammad...
Could you change the top "Continue" button label on the post preview page to "Submit Post" or something like that? I wasn't going to say anything as long as it was happening just to me but now that a similiar problem may be occurring with others you may want to consider the change. Just curious.
Kelvin