I think its because superSU root is systemless, and the root checker is looking for su binary files inside /system.
I don't know why this is happening... Last time I was using stock JB, and I changed the lockscreen for the ICS one... I'm sorry I couldn't help you :(
You can use the UxpNxtLockscreen.apk of any stock rom. You just need to replace the one of the rom you have :)
Awesome job, but the facebook contacts don't appear in the contacts list :S