This does not appear to be an API bug. Is it?

not a blocker, delayed.

This has been fixed in CVS:

2005-12-12  Wim Taymans  <wim@fluendo.com>

        * docs/libs/gstreamer-libs-sections.txt:
        Added new symbol to docs.

        * libs/gst/base/gstbasesrc.c: (gst_base_src_class_init),
        (gst_base_src_init), (gst_base_src_set_format),
        (gst_base_src_default_query), (gst_base_src_query),
        (gst_base_src_default_do_seek), (gst_base_src_do_seek),
        (gst_base_src_perform_seek), (gst_base_src_send_event),
        (gst_base_src_default_event), (gst_base_src_event_handler),
        (gst_base_src_set_property), (gst_base_src_get_property),
        (gst_base_src_wait), (gst_base_src_do_sync),
        (gst_base_src_update_length), (gst_base_src_get_range),
        (gst_base_src_check_get_range), (gst_base_src_loop),
        (gst_base_src_default_negotiate), (gst_base_src_start),
        (gst_base_src_activate_push), (gst_base_src_activate_pull),
        (gst_base_src_change_state):
        * libs/gst/base/gstbasesrc.h:
        Implement seeking to other formats than _BYTES.
        Implement more seeking methods correctly.
        Doc updates.
        Added query vmethod.
        Added do_seek vmethod to make life easier for subclasses
        when seeking.
        API addition: gst_base_src_set_format()