The new version Sleep app does not stop tracking on my Venu.
It took me a while to discover that I need to long-press the menu button, bottom right, 2(!) times before the control functions are displayed.
But the pause and especially the Stop Tracking fields do nothing else than locking the app on my watch again.
Seems development expected this behaviour as they added a third option to kill the app. That one actually does work.
Next I reach over for my mobile, turn it on and tell the Sleep app to stop recording.
The excessive battery drain is now fixed!
I now have a ~3% drain per hour. I find that reasonable I guess.