let me explain
we have some Forest objects. so they have material and everything is ok.
when ever edit objects for Forest node they complete ok and no problem
but every time we merge the same object from another file with an alternative material, etc ... the 3dsmax ask a question
we need to merge material because we need update material from Forest object
but not update in Forest node.
we should press clear bottom in Geometry part to reload new material
so in a normal scene, I have over 20 forest and it took me many time.