The compare listing plugin has a bug with the thumbnail preview. When an user first adds a listing to compare. The thumbnail is not automatically generated and the title gives a "null" attribute.

Once you add a listing to compare, it looks like this:

Screen Shot 2013-03-01 at 4.16.12 PM.jpg

Then if you collapse the tab or go back to browsing then come back to view the compare tab, it loads fine:

Screen Shot 2013-03-01 at 4.16.29 PM.jpg