I had the Greybough hero and two Mama Bear.
After my Kindly Grandmother died the Big Bad Wolf got summon and got +4/+4 x2 from Mama Bear and +1 / +2 from Greybough spawning a 12/12 with taunt, BUT, then it got reduced to a 8/8.
The same thing happen with minions spawned from Rat Pack dying, each Rat got spawned with 10/11 and then got reduced to 6/7 (one of the times it got reduced to 8/8 instead).
I also tested selling 1 Mama Bear and playing a Pack Leader, and the same thing happened the Big Bad Wolf was summoned as 8/8 instead of 10/8, although same thing as above, one of the times the Big Bad Wolf got summoned as a 6/6 instead.
It seems to be some issue with the ordering / stacking of buffs.