Wireless iMouse cannot re-connect to mac via bluetooth

Here's my case:

My Macbook Pro is running Yosemite 10.10.3. The wireless iMouse connected to my laptop via bluetooth. I took away the mac long enough from the iMouse so that the connection was lost as the distance is too long to maintain the bluetooth connection. Then, I went back near to the iMouse and I suppose they could reconnect but they didn't.

Ways I tried to reconnect:

1. turn off then turn on the iMouse

2. turn off then turn on the bluetooth on my mac

3. select the "iMouse" from the bluetooth list on the mac os then click "Connect"

4. turn off then turn on both iMouse the bluetooth on mac at the same time

All of these didn't work. I guess there is a bug of the bluetooth connection if connect is lost by "not discoverable" rather than turn off iMouse or bluetooth on mac.

I found a way that can reconnect:

Logging out and then click the iMouse(try to reconnect from iMouse side) on the login page. I can see the iMouse is connected after a couple of seconds. Then login and the iMouse can work.

Based on this solution, I realy suspect that it's a bug of the Yosemite system as some information is broken during the connection lost so that I have to logout to delete users data which may block the reconnection.