OK, in fact the problem seems to be more general. It occurs each time the screen "go to sleep".
For more details, please see this question on askubuntu.com: http://askubuntu.com/q/760998/173553 -- You received this bug notification because you are a member of Ubuntu-X, which is subscribed to xorg in Ubuntu. https://bugs.launchpad.net/bugs/1574251 Title: Resuming from screen lock with a multimonitor setup causes all windows to migrate to the "primary screen" To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/xorg/+bug/1574251/+subscriptions _______________________________________________ Mailing list: https://launchpad.net/~ubuntu-x-swat Post to : ubuntu-x-swat@lists.launchpad.net Unsubscribe : https://launchpad.net/~ubuntu-x-swat More help : https://help.launchpad.net/ListHelp