In WPF pop up messages, drop down list appear behind main window

I am currently working on WPF touch-screen application. I am developing it on Windows XP machine. I have tested it on this mach开发者_如何学编程ine and it works perfectly fine. But when I deploy it to Windows Embedded machine I start to get strange behaviour: all pop up messages, drop down list, context menus appear behind the main window.

I am also setting the focus on my main window, when application loads, to enable context menu on the main screen.

Also my main window's AllowTransparency is set to true, (I have seen people had similar issues when having set to AllowTransparency). And also this didn't happen in the previous release.

Edit: The issues has gone after several compilations, I was unable to reproduce it, but I am still trying. I also think it has to be something related to graphic driver, as it happens on one windows XP machine, but not on another (hardware is different, one run XP embedded 2nd XP professional).

Any idea why this is happening?

Have you tried forcing the ZIndex of the elements to that they are higher than the main window?

This MSDN blog post describes it's use - but the important part might be:

The first set of Rectangle objects uses the default z-ordering rendering of objects, which is based on the position of the child object in the Canvas collection

So if the order the objects are created has changed (for whatever reason) you might see this behaviour.

Explicitly setting the ZIndex will confirm or deny this.