No pingbacks being recorded

I’ve been unable to figure out what I’ve been doing wrong with regard to pingbacks.

I’ve been running my blog for about 6 months, but my database shows 0 comments where the type is pingback. Yet I know that other sites have linked to my posts, and I’ve run tests from http://www.tamba2.org.uk/wordpress/TestTrack/. Still no pingbacks showing. I do get plenty of normal comments.

I’m running WordPress 2.1.3, hosted by BlueHost. In my wp options, I allow pingbacks and trackbacks. My active plugins are: Optimal Title; Peter’s custom antispam; Alex King’s Popularity Contest; and Text Control. My template is based on Andreas.

I’m out of ideas as to why I cannot get pingbacks to record. Any help would be greatly appreciated.

Thanks,
Adam