I noticed this last night while I was try to avoid some Frost Nova bombs from a Waller elite.
I could Whirlwind through the walls like they weren't there!



I love using Whirlwind as my escape skill since you can spin through enemies that would otherwise be blocking your path, but this may be a little too overpowered.

I believe that this bug was caused by Blizzard fixing an issue that was keeping Wizards from Teleporting out of a Waller's walls.
In fact, it looks like Blizzard is reverting this Hotfix because it broke Whirlwind:

•Teleport
•REVERSION - The following hotfix is being reverted:
•Should now properly allow Wizards to pass over walls created by monsters with the Waller affix.*
•This issue will instead be readdressed in a future patch.

Well, just as a test, after reading your post I can use Dashing Strike on monk to teleport through the walls.