I investigated this a bit - it looks like Unity tweak tool (which is completely necessary app with Unity due lack of proper options) sets every action in titlebar to toggle shader when you press 'Restore defaults', which is likely the reason why this happened to my installations.
Nonetheless, doesn't seem to be Unity bug, guess this should be assigned for the tweak tool devs.
It says 'toggle-shade', so yes I guess so.
I investigated this a bit - it looks like Unity tweak tool (which is completely necessary app with Unity due lack of proper options) sets every action in titlebar to toggle shader when you press 'Restore defaults', which is likely the reason why this happened to my installations.
Nonetheless, doesn't seem to be Unity bug, guess this should be assigned for the tweak tool devs.