Window SizeToContent issue

[tNRevan]

Hello,

I am having issues, when WPF Window.SizeToContent = WidthAndHeight. I have a simple window with stack panel and few items where one of those is managed by GridExtra. When I open the window, it looks like this:

The individual items are overlapping as the GridExtra uses wrongly the LG format (with 4 items on one row). When I just tap the window resize edge, the Grid produces a correct result using the XS format (1 item per row).

When manually enlarging the window, it is laid out correctly.

Am I doing something wrong? Is this a bug? Or is this just not supported? If there is a need, I could produce a sample application.