After locking my Mac and waking it up a few hours later this is how it looks:
Also, some of the icons look weird after restarting the system (for example not fully rendered time machine icon: )
Hardware: mid 2013 MacBook Air - i5 1,5GHz 128SSD, 8GB RAM.
I suspect one thing, however this is my first mac and I prefer not to mess around anymore: The problem started ocurring after I have disabled the swap.
Earlier I did research how much memory I use (<4GB RAM and ~2GB swap) and decided to remove the swap to force RAM usage.
What could be causing this behaviour?