Larry, I don't know what the problem is but hear me out, I'll give it a try. Your playing time of asteroids is "probably" exceding the maximum idle time thereby logging you off. I know that your not idle otherwise you would not get high score but the S-B site maynot recognize games as activity if you know what I mean. Also JohnR can't duplicate the problem because he is not playing as long as you because he has a life.
I have experienced being logged off after I compose a post then it says that I have to log in. Maybe I take to long but that what happens.
When you log in do you check "remember password" box, maybe that could be the problem.
Good Luck