Assume that you have some sort of external SharePoint content type of entity Test. The Test entity has a property associated with it called SearchUrl which when crawling the external content type will have the bdc3:// prefix, to control this you have to implement the DisplayUriField in both of your Finder and SpecificFinder methods. But even AFTER you do this, the URL will still use the bdc3:// prefix. Whats going on?!?!?!
The solution to this is to restart SharePoint Server Search 14 windows service which will force it to pick up the latest version of your assembly.