Example will be best here: Profile of Pnina Lugassi (פנינה לוגסי), See:
http://www.geni.com/family-tree/index/6000000003633574920
This profile have Hebrew-only, first name, surname and birth surname.
No matter what the Preferences->Display->Names are, the birth surname is NOT shown. Only first+surname.
1. If you enter English data - it works fine (the English is shown correctly)
2. If you enter also Hebrew display name, but same as the default, i.e. "first last (birth)" - it is greyed in the form and NOT shown in the tree.
3. If you enter non-default Hebrew display name - it is displayed (according to the settings)