Multi-Screen Problems after upgrading jessie -> stretch

[Jan Luehr <debian-list@jluehr.de>]

Hello folks,

I've some trouble with multi-screen setups changing while logged in - ie
due to:
- a data projector is connected, disconnected or reconnected
- a docking station is docked / un-docked

In all situations:
- xrander lists all screens correctly
- System Settings -> Display Monitoring shows the connected devices
correctly.
- Suspending / uns-uspending has no effect
- If switching to a text-console (CTRL+Alt+Fn) the console is shown on
all screens correctly. When switching back, the desktop is show for a
fraction of a second (buffer?)

Problems occurring:
- New screens remain black (ie: Plugged in data projector remains black)
- Old screens are not detached (ie Desktop occupies non-existing
screens, menu bar is missing).
- All screens are black, the mouse pointer is shown, only.

Misc:
- Restarting the xserver helps usually - the current layout is applied
correctly
- Deleting .local/share/applications/kscreen and the old
.kde-kscreen-directory has no effect
- Jessie was ok - all problems are regressions after updating to Stretch.

Do you have any idea how to fix that ?
For the moment, I need to restart my session (Log-In / Log-Out), when
giving a talk or the connection to the data projector is lost for a
second during a talk. It is really annoying. :-(

Thanks in advance,
Jan


-- 
For those of you without hope, we have rooms with color TV,
cable and air conditioning