[Koha] Problem when removing subfield in biblio editor

Hi, Does anyone of you recognize this (rather serious) problem. If I have a field say 710 with $4 relator code followed by $9 authid and $a name, and I clear the $4 with Delete this subfield and save the record, I also loose the other subfields!! This does not happen when the subfield order is different like $9 $a $4 and clearing $4. Came across old Bugzilla reports 3264 and 5707 but they seem to focus on authorities editor. This problem above is in the biblio editor. Any comments welcome, Marcel