i can not login again on lock screen,when the virtualbox session is working

[Rainman.Liu]

1.I run the virtualbox manager,and play one virtual mechine;
2.then i leave the seat to do something;
3.when i come back,the lock screen is working;
4.but i can not input the password to unlock the screen;
5.i enter the other tty, ps aux | grep virtualbox, kill the associated proc id；
6.when i continue to x window, sometimes i could unlock the screen,sometimes i still couldn't the screen unless i choose switch user;
7.when i return the system, the network can not work. i only reboot the syste.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.