Thresh and Frost Queens Claim interaction

Okay, so on the forums I have yet to see a post about this, and I'm not exactly sure if its intentional or a bug. Anyway, if someone casts a frost queens claim and thresh is on the other team, if the ghouls do not reach a target, they have a chance of dropping a soul as they disappear. So far I've only been in 1 game in which this happened, but its not often I see a frost queens and a thresh in the same game, so I don't know if its a normal bug or a random 1 time glitch.