I have experienced the same problem. I can reproduce it all the time in the following way:
1. Focus any application
2. Press and hold alt
3. Tap F10 a few times
4. Release alt
After this, unity is broken and unusable - the only way to get it back is restarting compiz. It seems rather critical. Currently I'm using unity 5.4.0+bzr2064ubuntu0+654 with compiz 1:0.9.7.0+bzr3035-0ubuntu1~ppa3. My system is an i386 with the fglrx graphics driver.
I have experienced the same problem. I can reproduce it all the time in the following way:
1. Focus any application
2. Press and hold alt
3. Tap F10 a few times
4. Release alt
After this, unity is broken and unusable - the only way to get it back is restarting compiz. It seems rather critical. Currently I'm using unity 5.4.0+bzr2064ub untu0+654 with compiz 1:0.9.7. 0+bzr3035- 0ubuntu1~ ppa3. My system is an i386 with the fglrx graphics driver.