Essence Mob stuck in catapult > unkillable

Cheers

First of all here is the bug reference number: 356.250.056

I came across this when I ran a Blue Ramparts Map.
On the top of the wall, a Essence Mob was standing inside a catapult. Normaly you would have several monsters trapped in crystal around it but this time it was just the mob holding the essence.

I could release it (as you can see from the screenshot) but I could not dmg it.

http://i.imgur.com/rIFoJd7.jpg

Best regards
Sephira

Similar happened to me. Essence mob got stuck instead unbreakable object. The mob was not kill-able nor could it damage me.

http://imgur.com/a/ppEh7