Ubuntu phone: Power button - screen wakeup bug

I have experienced the issue below on my Nexus 4 since October 2014. Now it has appeared on my Bq Aquaris e4.5 approximately 3 weeks after I got the phone. I am currently running Ubuntu 14.10 (r20).

Often, but not always, when pushing the power button to make the screen wake
up, nothing happens. After waiting a few seconds, I push the button again
and the screen wakes up for a fraction of a second and then turns off. The
behavior suggests that the second time the button was pushed it was
registered as a "switch off screen" command. This can repeat itself a few
times. Usually, I have to push the button slightly harder/more decisively
(perhaps a hint longer) in order for the screen to wake up and stay on. The screen will eventually come on after pushing the power button an odd number of times, never after an even number. Very annoying!

I have tried just waiting for the screen to come on after initially pushing the power button, but my patience usually wears out after 10-15 seconds. I once waited for half a minute.