Joe,
The ID has changed because you have changed the assigned material. So that if the new material had different parameters it would know the difference. It has been noted that if you use this context, you can refer to the current active material.
Your relation for Material Description would be:
MATERIAL=material_param("PTC_MATERIAL_DESCRIPTION")
So in your Flange Width Example it would equivalently be:
WIDTH=material_param("FLANGE_WIDTH") to get the width for whatever material is currently assigned.