My Opponent had played Valgavoth, Terror Eater and ended his turn.

Starting my turn with Ugin, Eye of the storm and Jace Reawakened with 6 loyalty counters on him on my side of the field i activate Jace's action "Until end of turn, whenever you cast a spell, copy it..." and play Buster Sword, which activates Ugin's action "Whenever you cast a colorless spell, exile up to one target permanent that's one or more colors."

I exile Valgavoth and pay his ward costs by exiling 3 permanents.

Jace's action copies my Buster sword which should trigger again Ugin's action to exile a target permanent.

Instead of activating Ugin's action again suddenly my turn ends with two buster swords on my side of the field and my opponent's turn starts without me being able to do anything. WTF is this? Why could i not proceed with my turn?
Please investigate attached log and fix this bull****! It seems like Valgavoth is totally bugged. REMOVE THAT CARD IF YOU ARE NOT ABLE TO MAKE IT FUNCTION PROPERLY! Otherwise anybody could just exploit Valgavoth because it seems not removable.