Same experience here! Me, too.
I sometimes minimize POV-Ray, and when maximizing it again, whoops - the
render window is back. ;-)
But sometimes, when often stopping and restarting a render entirely, all
render-related buttons are disabled - I cannot start a new render
anymore with - indeed - restarting POV-Ray. I call this bug the
"Uncertain POV User Bug" as it seems to punish those who stop and start
renders often... :-D
