I'm not sure, sorting by date added still keeps all the tracks within each album in the correct order (all the tracks have the same date & time added hence MB must subsequently default to track# to sort), however its just the albums which are not listed in the correct order. Some new albums I've added a day or two ago are appearing at the bottom of the list.
The other thing is that if I select the Tracks view, then everything is correctly sorted via date added. If you go back to album / tracks view and you click on any field to sort eg track# or Track Title, everything is correctly sorted numerically or alphabetically. It just seems limited to date added / modified that things aren't sorted properly. Pulling out my hair trying to find a pattern as to why this is happening!