I have the same problem... !!
I've had it on other ROM's before, but not sure exactly what caused it. I can remove icons from the launcher dock, but cannot add / replace them with anything. They seem to stack up on the dock, but do not actually launch anything.
Running CarbonROM -- Nova Launcher seemed to be ok. I added a coule modules to Xposed Framework, but haven't been able to figure out exactly what broke it yet. I'll keep messing with it. If I find the solution, I will let you know.
If anyone has any input, please advise!
Edit: I disabled all of the Xposed framework modules+reboot -- still didn't work. Uninstalled all framework modules and framework+reboot then uninstalled+reinstalled nova launcher. I still have the same problem, but it's not a problem directly related to nova as I have the same locked dock issue with all launchers. Going to restore from a backup and see if I can recreate the problem.
Update: Apparently the only backup I had had a broken dock also, so it had nothing to do with anything in Xposed as far as I know. I sure would like to know how to fix it if it ever happens again tho!