The Telerik.Windows.Themes.Windows7 assembly reference was missing in the project.
The window was shown with related theme applied in XAML, but the window behaved strange.
The properties that have been applied in style before did not work after setting the theme.
These properties started to work after they are moved from style directly to the window itself.
One of these properties are WindowStartupLocation, Width and Height.
It seems to me that the settings have their priority:
1.) Some properties (not all of them) in XAML itself have the highest priority,
2.) Then the theme properties are forced,
3.) The properties in styles have the lowest priority.
I'm asking myself am I right. Can you clarify that if you know the cause?