Check you haven't turned on "transparency" by hitting 'ALT'+'X'.......it's easy to do without knowing. Just hit it again to make sure. If you have separate objects in the model only the selected one will be affected, the rest will continue to display the material.
By default, Max assigns Mat ID's in increments to each new object, that is to say if you convert three objects to Ed-Poly, then the first one created will have all poly's as ID1, the second object ID2 and so on. Each new poly object will therefore have poly ID's of one higher than the last, which will explain why your 'new' poly's are ID2..........are you sure you are adding polys to your existing object?
Don't get confused here though, Mat ID's only relate to Multi/Sub-Obj Materials......if you haven't applied a Multi/Sub-Obj material to an object then the ID's are irrelevant anyway......which leads me to belive 'ALT' + 'X' may just be your answer.
Failing that, post a few screenshots and a description of exactly HOW you are adding more geometry....it will help us to understand more clearly what the problem may be.
Regards.