The new 1.4 version of flatty template has issue with the newest compare plugin. Basically, you cant click on the "add to comparison table" icon when viewing a specific listing. You can however click on it when seeing a list of listings. I have tested with all flatty realty, auto, general, same problem. When switch back to my modern template, it works fine.
P/S: tested on demo site, works ok. Tested on my fresh installation with 1.4 has that issue.