dual screen window problem

Hello there !

need some help.

I use Krypton (RC just out), I’ve got a little problem.
I play with a mac mini (latest os) with a monitor (1920×1080) and a 4K TV (but keep it in 1920×1080).
I tell kodi to use the TV as it’s default screen. Kodi 16.1 do the job great. I can watch movies via kodi on TV and working on monitor in same time.

But since Krypton version, when I start Kodi I get a strange grey window floating on my monitor.
see image capture first screen

Kodi 17 RC runs good on TV but it remained this window on the monitor. I treid many things in preferences without success…

Anyone else ? Help !

Thanks.