Twice now in my current game as the English on a Cold Archipelago world the natives have demanded 25 muskets for some imagined atrocities (honest I never touched them!) and I handed them over. What's buggy is that they now have 50 muskets (F9 screen) each. That means they get 50 while I lose 25. Doubling going on here. Bug I guess. I wish they'd just take all 50. 25 aren't much use to me.

It must be that giving the natives a single musket automatically equips one of their marauding units (thus, 50 muskets).

Frankly the armed braves are a beautiful thing. Find the coastal cities of natives who suffer border tensions with the other European powers. Take your ships and sell them as many muskets and horses as they will take (which can be a couple shiploads), and listen to the sweet music of native tribes sacking the European colonies. Mounted warriors in the early stages of the game will have their way with anything!