Unless the committee/forum is very, very formal, refer to the chair by
his/her title + surname, but otherwise, as the others have suggested,
leave it well alone. When *you* get appointed as the chair of anything you
can change your own title immediately and set a good example.
Or you can insist on being called 'Madam Chairman' upon your appointment.
If this bit of departmental foolishness is really getting your goat you
may actually be quite angry about something more substantive. If that
resonates as 'true', get cool-headed and identify what that more
substantive thing is, and plan your campaign/s accordingly.
and good luck!
Dr. Katherine J. Kaye
School of Geography
Oxford OX1 3TB
ubi Deus, ibi pax; ubi caritas, amor.