Comment 71 for bug 1255558

I've pushed a branch to lp:~robert-ancell/lightdm/wm-log that logs some information (will be in /var/log/lightdm/x-0-greeter.log) about when u-g thinks windows have appeared/disappeared and who it gave focus to.

The branch Alberts made seems to indicate it might be something in this code causing the problem.