Which I don’t mind. But then the TDM needs to be reduced.
Tested Ascension duration extend on ascended mods, works fine.
Ascended bonuses for Fighting Spirit are also still refreshing the duration indefinitely.
how exactly is the (new) duration extension supposed to work
Because while arcane will modifiers doesn’t seem to extend it indefinitely, also doesn’t seem to follow all its increased “cap”/duration extension either 
i’m getting 16sec duration where before i got 28sec Warlock, Level 100 (GD 1.3.1.0) - Grim Dawn Build Calculator