It's a safe assumption that when a user presses a power button, they intend that the device be immediately turned off or shut down. I can't think of any device that performs any differently. If a user wants to shut down vdr after he's done watching a playback, he would obviously still be sitting there when it ends therefore he can press the power button when its over.
I see no reason to make this issue more complex than it should be. The power button has the final say, you don't press it if you don't want to force a shutdown. What logic is there that vdr should be any different?
Just my $.02 fellas.
Cheers!