While adding new password or updating an existing one. It occurs only in "Tags" field - when highlighting the text inside (or portion of it) with Shift + [arrows or Home or End], highlighting lasts only for so long as Shift-key is pressed down.
Highlighting should last after releasing Shift and until pressing another key, same as in all other fields.
Differences between New password and Update password actions:
In "New password" first editing of "Tags" field works as expected. After focusing to another field and then to "Tags" again, the described (wrong) behaviour is observed.
SuSE Linux, kernel 18.104.22.168-0.1-pae i386