Slingblade Demon - Bug?

[BigChief]

I was playing Gravebone vs Boris.
I had a Kairos Doombringer on the field, who had a Crippling Blow attached to him. Kairos was brought to play through Gravebone's ability, not summoned.
I cast Slingblade Demon to return him to my hand (and cure his affliction) but I was not able to target him at all.
I was still able to target the other 3 allies I had in play, such as Sun-Blighted One and Harbinger.

This seems like a bug. Otherwise, please tell me what I don't comprehend about SB Demon's ability.

[Romantic Gunner]

Kairos Doombringer has Steadfast which prevents it from leaving the field unless killed.

[matei13]

Kairos has steadfast. He cannot leave play unless he's killed. That's why you weren't able to target it.

[BigChief]

Yep yep forgot about Steadfast! Thanks.