It works. Be sure that you're looking at the bonuses correctly. Remember that it only boosts the Mundus Stone effect by a percentage; it doesn't add on to it. For example (numbers made up in order to simplify things):
Mage Stone Buff: 100 Magicka
Divines gear bonus: Let's say 12%
New Mage Stone Buff: 112 Magicka
So if you're applying it to a stone like the Thief, which adds a single-digit percentage chance to crit, the effect is going to be quite small.
I've found that Divines coupled with Thief tends to be a bit intermittent in how it works. When I logged in after the patch it wasn't working then a couple of days later it mysteriously was.