Every bug is different and differently affect gameplay or don't affect at all and all of this are subjectively, so people will start argue with us about how much bug affecting game just to get better reward...
Checked, working correctly. Without rune MP regen ~17. With Rune ~19. ( 17/100*17+17 = 19.89 )
And yes, it's not recharge regen, it's passive MP regeneration when you are standing or sitting.