Until Creo 4.0 we were using the Attribute PTC_MATERIAL_DESCRIPTION instead of PTC_MATERIAL because for the latter you only get capital letters, the "description" can be according to (ISO) standards and include lower case.
Starting with Creo 7 there is multibody now with the possibility to define more than one material per Part.
If one wants to designate only the material assigned to the model, and none of the materials assigned to bodies to the drawing frame one has to use the Attribute "PTC_MASTER_MATERIAL" which only includes Capital letters.
To work according to standards, lower case letters are needed. This is why the Attribute "PTC_MASTER_MATERIAL_DESCRIPTION" is needed.