I think I've encountered a bug in the Classifieds plugin. When we try to post a new ad, with a featured image, the ad gets posted, but the featured image doesn't get attached.
The image does upload into the site, but it doesn't attach to the post so it doesn't display. I have tested this by deactivating all the plugins except Classifieds and BuddyPress. I've also conducted the test against 3 of the default WordPress themes. The behavior always remains the same. The ad gets posted, the image uploads but fails to attach to the ad.
The live site for this is a protected intranet site, but I have a development/staging site that is a functional copy of that. It is http://dev.prometheusfire.me/act-connect/
I have opened up support access for the site. Feel free to run any tests you need to to verify.
UPDATE: I should clarify a little more. In the media library, the image shows as attached to the post, but when you view the edit screen for the ad, the featured image is not set. So I suppose that the image is getting technically "attached", but not set as the featured image.