Change line weight on shape - can't figure out how to allow on the master

[lizat]

I have created a copy of the BPMN stencil. There is a shape - a rectangle with rounded corners, which I have used as the basis for a new shape. It all works except that the user cannot change the width of the box outline. I have tracked this down to the Line Format settings on the shape sheet, at least i thought it was this. I changed the value to THEMEVAL(0) and hoped that would allow me to change the line weight.

However, although I can change the line weight and the Line Format for the specific shape (as opposed to the master on the stencil) shows the new weight the actual display doesn't change. So there is obviously something else i need to do.

Any ideas please?