Based on codePlex disscussion https://wpftoolkit.codeplex.com/discussions/532408.
When a Property is expanded, its Categories are not shown.
Comments: ** Comment from web user: yourbuddypal **
When a Property is expanded, its Categories are not shown.
Comments: ** Comment from web user: yourbuddypal **
I also have this issue. It is very annoying not having items sorted and grouped properly.