Bolas’ Omnipotence stops Karn’s 1st ability from fetching
You sure its that and not ol’Fibbles?
If it is, that’s definitely a bug, since the ability reads “fetch” and not “draw”
I’m pretty sure that I have fetched with Karn under a Bolas’s Omnipotence before. I’m inclined to believe that it’s a Fblthp bug rather than a Bolas bug.