This isnt by chance after you have been logged in and "inactive" for a while, is it? The system has a "timeout" period and will log you out after being inactive for a certain amount of time. If that is not the issue, then you should report it
I thought that could be an issue when I was experiencing the problem so I copied all my work and logged out and back in. Then pasted it right away and tried to post. Still didn't work, so I reported it.