This is what I see on 20.11: - I have a catalogue where searching for "perl" gives 5 hits. The URL for the search has opac-search.pl?q=perl - I tag two of the five records above with "perl" + one record that is not among the five, so three records are tagged with "perl" - Searching for "perl" still gives five hits, as expected - Following a link from the tag "perl" gives me three hits, the ones that are tagged with "perl". The URL has opac-search.pl?tag=perl&q=perl. I was expecting the last search to give me 6 hits, the union(?) of the five records that contains "perl" and the "extra" one that is tagged with "perl". Am I just remembering wronlgy how this used to work?
You can't search for tags in the catalogue search or mix the results like you expected. The 'perl' link lead to a tag search, so giving you only the tagged items. The search issue is filed as bug 5993.