Why do I lose my Bluetooth Mouse connection whenever I close my laptop?

It’s a Dell Inspiron 1525 with built-in Bluetooth capacity.

I have the power option set so that closing the lid powers off the computer.

When I do this and re-boot, though, the mouse does not work. I have to go into the Bluetooth Devices screen, uninstall the mouse, then re-install it. Then, it works again.

When I power off by clicking Start>Shut Down, then re-boot, the mouse works fine.

Any thoughts?
mmm