Comment # 166 on bug 1188970 from Stefan Dirsch

Ah. Ok. For waking up the monitor you changed the monitor layout. Now I
understand. 'xrandr --auto' may have the same effect though without changing
the layout. Anyway, both can only be called a workaround. And this will be an
issue hard to fix. Not sure if Thomas can reproduce it. Probably he won't.
Could be that the used desktop can easily workaround this issue by running such
an xrandr command after a resume automatically, but I don't know which desktop
is being used here ...