I have similar experience on AMD A10 6800K / ASRock FM2A85X-ITX, it
started with approximately kernel 3.12.5 ... F20 (I think, might be a
bit off on the version), It specifically effected the HDMI monitor on a
3 monitor setup. To work around I wait until the display finishes
switching to graphical screens, at which point the HDMI has no output.
<crtl><alt><F2> (KDE and Gnome act the same in this issue) to switch to
text mode, wait until finished switching, then power cycle the HDMI
monitor. <alt><F1> to switch back to graphical mode and the system ran
ok. Switching back to 3.11.xx series kernel made the regression disappear.
May not be related, but has similar characteristics.