Dual screen don't come back after session locked

[inkbottle <inkbottle007@gmail.com>]

My computer is a laptop with it's lid closed: I use an external monitor with a 
higher resolution.
Since last upgrade, when I lock the session and obviously leave the computer 
for some time; when I come back and move the mouse:
The "password field" is moved/shifted to the upper left, as if to fit the 
resolution of the "laptop built in screen", the mouse pointer is moving, but 
the keyboard doesn't work, I can't enter my password.
If then I open and close back the lid of the laptop, then I can use the 
keyboard again, and enter the password, with success.
However, then I don't have a fully functional Kwin, I don't have neither panel 
of background, for instance: I couldn't open a terminal if I hadn't one 
already opened.
Since I have one I type:
qdbus org.kde.ksmserver /KSMServer logout 0 0 0
to logout, and then everything seems fine till the next time.
It seems it does that always since last upgrade.
The laptop is a thinkpad, so I do have a Intel HD graphics card.

Thanks,
Chris