It's not a bug, i dont believe that shield is considered as a seperate class when it comes to requirements.
As for your ability to get rank 40 leves before the patch, before the change the minimal rank for attaining a leve was -7 ranks.
Ie, every 3x ranks. Since your glad is 34, your gladiator was a high enough rank to get the rank 40 leves (requirement of rank 33), before the patch, however its now rank 35 requirement, so your glad is one rank to low.

To sum it up, your available leves were never calculated by shield rank in the first place.