AT fluid from fill plug drained too much!

I am in need of some help trying to figure something out with my recent automatic transmission drain and refill on my 2003 325i with GM trans. Initially when I removed the fill plug, about a quart of more poured out! (my car was leveled and the engine was slightly warm. After I removed the drain plug to drain the rest, there was about 5 1/2 liters collected. My question is, why was there fluid coming out heavily from the fill plug when removed? Shouldn't it have just been driping or trickling out of the fill plug since the car was leveled? I was only able to put back 4 liters of atf fluid and am super confused as to why it wouldn't take the extra liter.