Strange issue with windows/tab Unreal Engine

Hello everyone

I have a strange issue with the tab or window. I do not know if it’s is a bug.
Since I crashed, I have a new black window in the background.
I do not know how to fix this.

I have this problem since the update 4.4.2
Note that if I close this window I also closes the software too
Thank you for your help.

EDITED :

I found a solution to fix it : Windows => Reset Layout
but it is hard, if I move the first tab, even this background
Thank you