Problem creating discussions for sessions

I'm not sure whether the cause of this problem lies in the conference_organizing module, cck, or elsewhere, but when I submit a new discussion for a conference session, the discussion is created, but field_related_session_nid in table content_field_related_session is always set to 0, rather than the corresponding related session nid.

So, I threw in a backtrace into cck's content.module via the devel module (see attached). I'm pretty new to drupal development and my php is pretty entry-level and rusty, but the following snippet jumped out at me:
[field_related_session] => Array ([0] => Array ([nid] => 0,[error_field] => field_related_session][nids))

It looks like there should is an open and close bracket missing around field_related_session and nids. The nid of the session to which I'm adding this discussion is 9, so perhaps it's already buggered by this point, anyway.

Additionally, the Related Session drop box lists "<none>" (only) when I go to edit a discussion, so I'm unable to set the related session even after I've created the discussion. The dev render tab for the discussion reveals the following:

field_related_session
Array(
[0] => Array(
[nid] => 0
[view] =>
)
)
I guess I'm wracking my brain on this one and it's a bit of a showstopper for my conference. Any help is appreciated.