Description of problem:

GTK3 applications intermittently stop registering mouse scroll wheel events in KDE Plasma as shipped in Fedora 22. I wasn't sure what to file this against, but I see another user has reported it appears not to be a libinput issue. I can reproduce it most easily using Firefox. I see there were two other users who reported this issue, but both their bugs have been closed due to difficulties reproducing it. (https://bugzilla.redhat.com/show_bug.cgi?id=1206549 and https://bugzilla.redhat.com/show_bug.cgi?id=1224465) I can reliably reproduce the problem every time.

Version-Release number of selected component (if applicable):
kwin 5.3.0-2.fc22
firefox 38.0.1-5.fc22

How reproducible:
Always

Steps to Reproduce:
1. Start KDE Plasma session.
2. Open Firefox. (The default Fedora Project home page suffices for this example.)
3. Observe that the scroll wheel works fine in Firefox.
4. Open Kate and operate the scroll wheel.
5. Close Kate.
6. Return to Firefox and find the scroll wheel no longer works.
7. Interact with other applications (open up something else, like LibreOffice) and use the scroll wheel.
8. Observe the scroll wheel once again works in Firefox.

Actual results:
Scroll wheel stops registering events.

Expected results:
It should work normally.