Collectible Card Game Headquarters

Seems like when computer puts a triggered ability on the stack, I am not allowed to cast instants as response unless I activate an ability first(tapping a land and then undoing the tap makes instants castable again as well.)

If you put a triggered ability on stack, everything works normal(for you.)

I have realized this first with Blight. Computer put Blight on my Island, I tapped enchanted Island and computer put the Blight trigger on stack, and then I am not allowed to Rescue the Island with the floating blue mana.