Comment 5 for bug 229123

Looks like I was able to significantly narrow down the problem.

I have both an USB keyboard and an USB mouse. Keyboard was mostly working as previously stated, but mouse usage was a problem.
Since my keyboard is dual USB/PS2 and i have an USB to PS2 adapter, I proceeded to connect both my keyboard and mouse via the PS2 connectors.
A quick reboot later and I have not seen any more of those focus problems that were quite persistent.

So, that means this problem is related to X and USB HID-devices.