I am currently wearing the level 80 Spooky Carnival Hat which I simply stitched to a different look, but retained the stats. Therefore, I have 8% stun resist on my wizard.
The "New Moon Priestess" used Medusa on my wizard and I was lucky enough to resist the stun indicated by the game displayed "Stun Resisted!". Although the game displayed that I resisted the stun, for those next 2 rounds every-time I selected a card for the round, the game simply passed my turn. The game did not say "Stunned!" like usual (which makes sense as I wasn't stunned), it just passed my turn.
After 2 rounds I was able to cast spells as per usual.
To conclude: Medusa's stun is currently bugged with stun resist statistics from gear.
The same thing happened today in the Atlantea dungeon when an Atlantean Trierarch casted Frost Giant on our group of 3. I resisted the stun, but the game passed my turn. Same gear, same stun resist, same issue as above.
Atlantean Trierarch casted 
Same gear, same stun resist, same issue as above.