Hi @C4DS , maybe I wasn't enough clear.
you end up with a single merged object, which has 2 selection tags, and both still have the specific name ... but none have the added unique ID. Surely you start to think something is really wrong.
Actually you end up in a new mesh with new selection tags which beside having the data copied from the two source selection tags, they are NEW and hence the UniqueID is not supposed to be kept. The names are kept for convenience but I don't see any reason to have also the UniqueID being kept considering that - in the end - they are indeed new instances and have nothing to do with the source selection tags.
Cheers, R