onboard doesn't response with wine application

Bug description:
When a WINE application is open with "Maximized" status and without "FormBorderStyle" the Onboard keyboard loses the focus and stops receiving touch events.

C# (WinForm) main Form configuration (running on WINE):
FormBorderStyle = System.Windows.Forms.FormBorderStyle.None;
WindowState = System.Windows.Forms.FormWindowState.Maximized

Expected behaviour:
Onboard keyboard keep receving touch events.

What happened instead:
Onboard keyboard stops receiving touch events, to make it working I need to press Ctrl+Tab (or Ctrl+WIN) on a physical keyboard.

You have any idea?

[Xorg][Linux version Debian 9.0][Wine Version 4.0]