I deleted some tracks (one album) from the Library but not from the hard drive and am unable to re-import them. All settings are as they should be and "Ignore files previously removed from library" is not checked. I did the same in 11 just to check and they re-import without any problem.
Edit: Just to make sure I could re-create the problem I removed another album in 12 and cannot re-import it. Did the same thing with the same album in 11 and it re-imported perfectly.
Thanks