It does not do that, but it can seem like that. It goes blurry and then you are tempted to play with the focus again. And then you keep adjusting till you once again get a few moments of better seeing and think you got it back in focus. But 30 secs later it's gone blurry again because the seeing got worse. So you go back to playing with the focuser and so on and so on ... drive yourself bananas ...
I know. I've been there, done that.
