It’s happened to me more than once that after merging two items (mostly CD1 with CD2 of an album), I then move on to the next forgetting to deselect the previous and continue merging CDs…you can easily imagine the mess that makes!
I see no reason when the selection should remain after one has made a merge because, as I explained, how often and why would anyone then want to merge that just-merged item…with another…and another!!?