Adding/Removing items in the Dropdown Menu (DDM) should not reset any keyframes or expressions in other comps when using Master Properties.

Likely, anyone using the DDM w/ MPs is doing some complex rigging, and having to start over from scratch if you need to add an option breaks almost any usefulness from being able to combine these awesome features!

A nice UX would be to ask if you wanted to reset any keyframe or expression data, or let you choose to leave it, and deal with any resulting consequences like expressions breaking, etc.