This seems to be normal. It happens with a lot of items including my cell phone. I do not think you can change it. I simply power-off after I plug it in.
It's their design. Your display timer will turn-off the screen. When the blue light comes on, disconnect, then turn the system off. Vision may want the unit on so we get notification, updates, while the unit is charging.
Sometimes we need Vision to comment on some of these questions. Or create a link from these questions to a FAQ site. Instead of relying on users. Ref: TRON, users screw it up!
I thought I read a thread where the VTab will recharge faster to a 90% charge with it in the sleep vs off state? I think someone observed a timing difference. Perhaps they will chime in here.