Why is the finish coming off while sanding between coats of polyurethane on glazed cabinets?
What type of paint/glaze? Oil or water based poly?  Check with manufacturer of the poly to make sure it's compatible with previous top coats. The ones I've called in the past have always been very helpful.

How long did you let paint/glaze cure before poly? Even though paint dries within hours it takes a while to fully cure. If you apply the poly before it cures you'll have problems with the poly curing. Should wait at least 7 days before applying poly. More depending on climate.