At Warrior in the Windmill skill there's an other skill called Prolonged Spin. It should increase the duration of Windmill by 25%. But after unlocking this skill the Windmill lasts shorter than before. Today I made a few new warriors and I saw this at all of them. I found this bug only at my newly leveled warriors. It seems like it's working fine at the "older" warriors that have every subskill unlocked at Windmill.
Now the charged Windmill stops immediately after two seconds!