I experienced a regression after upgrading Linux from Debian's 3.2.35-2 to its
3.2.39-2. As Ben Hutchings explained to me, that is because some Linux 3.3/3.4
graphics changes were backported in Debian's 3.2.39. And indeed, if I try 3.4.4
or 3.8.3, the regression remains.

I have only experienced the problem on KDE, but I didn't try other
environments. My laptop has a Radeon HD 5650 card connected to an LCD screen
via HDMI. When I leave the laptop idle and come back after a while, the screen
resumes. What changed is that I now get 2 KDE dialogs telling me:

A monitor output has been disconnected.

Do you wish to run a configuration tool to adjust the monitor setup?

immediately followed by

A monitor output has been connected.

Do you wish to run a configuration tool to adjust the monitor setup?

(The latter shows on top) Obviously, this is incorrect. I simply press Escape
twice and the problem disappears until the next time I leave the PC. This is
just an annoyance.

I ran tail --follow on .xsession-errors to debug and found as only clue the
message "main input error: ES_OUT_RESET_PCR called" logged twice. For example,
after a monitor resume, the following had been logged:

[0x85fc680] main input error: ES_OUT_RESET_PCR called
[0xf1b0a9b8] main input error: ES_OUT_RESET_PCR called

I noticed that this error is logged every time the system detects a monitor
(dis)connection, real or spurious (On my good Linux version, a resume doesn't
trigger that error). Oddly enough, I searched the web quite a bit, asked
#debian-kde and #kde and found no one with the same problem. The
ES_OUT_RESET_PCR error is common, but in very different contexts. This does not
happen when using the vesa driver, nor when modeset is disabled, nor when I
plug the screen via VGA (the laptop has no DVI plug to test). There are no
hints in system logs.

The KDE prompts above are the standard prompts shown when a (dis)connection is
detected. Debian testing's KDE version is not the latest (4.8.4).