As the title states, Haste has its original functionality even with Forgemaster’s Might. It simply gives me increased movement speed instead of the block chance.
It is not on the tooltip but maybe it works, who knows? No idea how to test this…
Assuming the tooltip updates properly for block chance, I can confirm this is a bug. To test you can run around with a pair of Advent of the Erased on. Open character screen and when you see the haste buff happen, check and see if you’re getting +10% block chance.