I used picard on a disc, open website, search for album title, add new release. On the tracklist page I opened the track parser. The entries were in the form "track title - track artist". Checked the checkboxes for "has track artists," "use track artists," "use track titles." Clicked parse tracks. Only the track titles looked as though they had been filled in. The track artists looked blank. If I click "close", artists remained blank. If I click Track Parser to re-edit, title and artist (and time) are filled in for the track parser but not in the main window. If I click parse tracks, artist remains blank. If I close and proceed to the next page, the tracklist page turns "red" and reports that there are no artists.
The workaround is to parse tracks, then click "swap track titles with artist credits" twice. After the first click, both columns are filled in, and the second is necessary only to get the values into the proper column.
Using firefox 60.6.3 esr on debian linux.
note: When adding more media, the track parser works as expected, i.e. both track title and artist are filled in. It only fails on the first medium.