Problem:
Currently when a Rectangle together with a large TextBlock is contained by a Shape where the Rectangle should enclose the TextBlock it is not resized by the size of the TextBlock, but the TextBlock is overflowing the Rectangle.

Possible solution:
Make the Rectangle a "visual group" so child elements like e.g. TextBlock or Image can be added to it and it will resize with the size of it's children.

Related Forum post: http://www.telerik.com/forums/how-to-avoid-text-overflow-in-shape