Strange, yesterday i had same problem:
At the start of my turn, I have 4 untapped lands.
At the beginning of the upkeep, the Pact of Negation trigger goes on the stack, and I lose the game.
I thought I could tap my Deathrite Shaman to produce mana.
You need to Hold priority to tap shaman
Strange, yesterday i had same problem:
At the start of my turn, I have 4 untapped lands.
At the beginning of the upkeep, the Pact of Negation trigger goes on the stack, and I lose the game.
I thought I could tap my Deathrite Shaman to produce mana.
You need to Hold priority to tap shaman