Are the bits that get crept into the project being asked for by the client? Are they valuable items to deliver?
There is certainly an issue with the PM if they are sneaking things into the scope and not making them visible. This is a serious concern and something I would raise with them directly and openly.
However, scope creep (in my book) is perfectly acceptable if it continues to meet the requirements of the business. Sure, you have deadlines, but what's wrong with being flexible on what you deliver on that deadline? This is where visibility is critical.