I can still see the material property in the feature manager, except when I right click it, the only options I have are collapse items, hide/show tree options and customise menu.  I can still go edit>appearance>material and assign a material there, or through SustainablitiyXpress so the library is not missing, however its a little annoying when trying to assign multiple parts with the same material in an assembly.  I have tried wiping the registry with no luck.