Bugs about Gruesome Menagerie [Investigating]

It‘s said that after using this card，you will return 3 creatures：highest cost less than 6 comes first，then cost 8 and cost 12.
But in game，it seems sometimes that highest cost less than 12 comes first，and sometimes cost 8 not come，and cost 6 comes 3times.
It is an big problem for me,please check it and fix.Thx

//Edited Title - Tombstone