[Bug] Eredon's Drums does not buff a card

Hello. For the second time I met a bug about artifacts in pandora mode.
The first time was with Disk of Time ([Bug] Artifact Disk of Time does not reduce the cost of a card).
Now, Eredon’s drum has annoyed me. ^^
Eredon’s drum has buffed every Creatures except one, an Angry Yak summoned by an Event.
I think it’s because it was summoned by an Event.
Poor Angry Yak, born as a 2/2, an still a 2/2 after Eredon’s Drums.

It’s definetly caused by Creatures summoned by effect, that happened to me a second time with a Ruby Fish summoned by a Gabrian Noble.