Comment 5 for bug 1499419

Although this is a dated bug report, I'm adding this note for others who might still encounter this bug.

I had the same Assertion 'kref' failed message when running some Qt 5.5.1 and Qt 5.6.0 webbrowser examples on Ubuntu 14.04 (32 bit). "nouveau" was the common factor.

After much searching around and finally reading a clue about NVIDIA I launched
Ubuntu Software Centre > Edit > Software Sources > Additional Drivers

wait until all NVIDIA drivers are found and displayed ..

NVIDIA Corporation: G86M [GeForce 8400M GS]

Under NVIDIA there were 6 drivers listed: 5 proprietary, 1 open source.

I was using .. X.Org X server - Nouveau display driver from xserver-xorg-video-nouveau (open source)

I applied a different driver (the earliest NVIDIA proprietary version)

NVIDIA legacy binary driver - version 173.14.39 from nvidia-173 (proprietary).

Rebooted. The bootup screen might be different.

I could then run the web browser apps in Qt Creator without nouveau crashing.