kubuntu 15.10: screen occasionally freezes when desktop lock is activated

[Kent Yoder]

Sometimes when I click the lock icon or activate screen lock with the hotkey combo to lock my desktop, I get the following behavior: the image on the screen freezes, mouse still moves but is unable to interact with anything (focus doesn't change, clicks have no effect). Once the display is in this state, I have to switch to a virtual console and reboot the machine to get a functional desktop back.

ProblemType: Bug
DistroRelease: Ubuntu 15.10
Package: kded5 5.15.0-0ubuntu1
ProcVersionSignature: Ubuntu 4.2.0-35.40-generic 4.2.8-ckt5
Uname: Linux 4.2.0-35-generic x86_64
ApportVersion: 2.19.1-0ubuntu5
Architecture: amd64
CurrentDesktop: KDE
Date: Fri Apr 15 13:35:16 2016
SourcePackage: kded
UpgradeStatus: No upgrade log present (probably fresh install)

[Kent Yoder (kentyoder)]

There's probably a 50/50 chance of the display freezing every time I activate screen lock. This makes the machine too unstable to use for day-to-day work.

Machine is fully patched.

[Kent Yoder (kentyoder)]

I've blacklisted the radeon driver and the problem persists. The other video driver is the i915 for the skylake integrated graphics.

[Kent Yoder (kentyoder)]

Installed gnome3 desktop and switched to it. The freeze issue has not happened since.