In GTK+, navigation between radio buttons in a radio button group is accomplished with the arrow keys. TAB doesn't move between radio buttons in a group, but rather moves on to the next control outside of the radio button group.  Further, when moving between radio buttons via the arrow keys, selection moves along with focus (so that the radio button you move to is also automatically selected).

The GTK+ L&F fails to do these three things.  Note: arguably the behavior of selecting when moving focus is not as good behavior for a screen reader user as the present behavior.  We may address this at some point in the future of GTK+.  However, until that time the best behavior is for the L&F to mimic as closely as possible current GTK+ behavior as showin in GNOME 2.6.

For an example of the proper GTK+ behavior, see the "Save Screenshow" dialog from the GNOME 2.6 desktop.  Also see http://bugzilla.gnome.org/show_bug.cgi?id=132182 for a bug describing the issue from the Gnopernicus screen reader perspective.
###@###.### 2004-03-04