Letho's banish ability useless against queensgaurd [possible bug]?

[rusty_warhorse]

Letho's banish ability useless against queensgaurd [possible bug]?

My Letho ate 3 of queensgaurd, and then sent them straight to graveyard! What?! How?! And the 3 of them keep coming back by resurrection, it made me lost the game.
Is Letho's ability useless against queensgaurd? And how is that?

 

[TV_JayArr]

It's supposed to banish them and it works gainst Queensguard.
Thus it seems to be bugged. Did something happened with Letho after/before banishing the Queensguard, that could have cause this occurrence?