Thunderbird 111.0b3 shows this behavior: # I select a line in the email-list. # I press key "1". # Thunderbird tags this email as "Important" and colors the selected line in red (screenshot 1), which is fine. # I select another email/line. # The previously tagged line is not colored red anymore (which is an error, I think - some days ago Thunderbird colored all "important"-tagged lines in red). # When I mark the previously tagged line, it's colored red again. So the tag information still exists. It's just not shown as long as the line is not selected.