There is some commented-out code to disable the save action when there are no files with unsaved changes in the file list selection. However, editing a tag field to be different to the value in the file does not mark the file as modified until moving to a different file, so just uncommenting the code breaks the use case of editing a text field and then activating the save action.

It should be sufficient to connect to the notify::text signal on the tag area entry fields, and to mark the file as modified if those fields change.

*** Bug 739758 has been marked as a duplicate of this bug. ***

GNOME is going to shut down bugzilla.gnome.org in favor of gitlab.gnome.org.
As part of that, we are mass-closing older open tickets in bugzilla.gnome.org
which have not seen updates for a longer time (resources are unfortunately
quite limited so not every ticket can get handled).

If you can still reproduce the situation described in this ticket in a recent
and supported software version, then please follow
  https://wiki.gnome.org/GettingInTouch/BugReportingGuidelines
and create a new enhancement request ticket at
  https://gitlab.gnome.org/GNOME/easytag/-/issues/

Thank you for your understanding and your help.