Support for transparent windows

[ScruffR]

I have got a WPF Inking application that can be overlayed ontop of any other application - e.g. to sketch off or annotate the display the underlying application presents.
However, when I try to use this application for a OBS Window Capture the application's screen is not captured at all, not even the non-transparent portions of it.

As soon the WPF Window control features the AllowsTransparency="True" attribute OBS Window Capture will only capture a black rectangle where the window should be.

 

[ScruffR]

Side note:
OBS can correctly capture WinForms windows with transparency (i.e. Transparency Key) - however the InkCanvas control to allow simple integration of pen support does not (easily) lend itself to WinForms applications.

I'm not quite sure in what way WPF transparency works that differently compared to WinForms with regards to OBS.