It isn't bugged.
I did some testing and it seems anythng below estimated 50% evade chance is pointless. but even at 50% it doesn't work like you would think.
At 44% evade I stood and let an enemy hit me, he hit me 21 times before he missed. Did it 3 more times with very similar results.
So, I went vendor shopping and found an Aura called grace, which, at its current level, grants aroundd 900 evasion.
Did the test again at 56% evade and got hit 9 times before missing.
So, still s***, I went looking for thing to help. I found a notable in the passive tree that grants 30% dodge. I didn't. test it but it seems better now, it seems I get hit 2 or 3 times then they start missing. Problem is the notable reduces spell dodging by 30%, so spells hit me nigh on everytime...but there is another notable 3 points away that give 30% spell dodge.
Honestly, this game is a mathmatician's wet dream. Forget string theory and time travel, the real mystery is PoE's stat system.