[xubuntu-users] Nvidia driver blanking out after monitor switch

[R. Vide]

I have two computers and one monitor that connects via DisplayPort.  The
Xubuntu computer has the Nvidia GT218, using the 331.38 driver from
nvidia-331-updates.  I just upgraded it to Xubuntu 14, and ever since
then, whenever I switch from a logged-in Xubuntu session to my other box,
then back, the screen is black.  After a few seconds the monitor display
pops up with the status "NO SIGNAL".

This all worked fine in Xubuntu 12.  Here are the details:

When I provoke the black screen problem, if I hit Control-Alt-Delete, then
hit another key, I get the unlock screen, at the proper resolution.  I
then type my password to unlock, and the screen goes black again.

If I instead hit Control-Alt-Backspace, I get the login screen.

If I hit Control-Alt-F1 I get the usual console login, when I hit
Control-Alt-F6 to go back to X we still have "no signal".

If I tell Xubuntu to use the X.org noveau driver, the problem doesn't
happen.  But then I have a different problem, namely being stuck at
800x600 resolution on a hi-res monitor.

There are four Nvidia driver options in the settings menu, the other ones
are for 304.117.  I've tried all four and no difference.

If I just leave the system on the main login screen, the problem never
happens with I switch out and back.

So whatever's happening seems to be related to my X session, so in theory
it should be fixable by tuning something.  If I only knew what it was...