Bluetooth Disconnection

[Burger]

I have a Viseeo MB2 fitted to my 2007 SL. It works perfectly. I'm curious though as to the disconnection time. Usually when I switch the car off and remove the key the phone will disconnect within a couple of minutes. Every now and then however it stays connected for a good 10 minutes. In order for it to do this the MB2 must be powered and on of course. Just wondering why the variable power down time of the cars electronics?

Thanks,