If i understand you request correctly, you want to be able to switch from a Cuelux pro mode control to a stand alone mode by desactivating the "mastering" of the CueCore in Cuelux pro?
But when you do i, even if the "mastering" is off, the Cuecore still appears as controlled by Cuelux Pro.
Am I right?
I tested it here, and the switch between Cuelux Pro and stand alone works fine.
Could you tell me the firmware version of your CueCore and send me your Cuelux pro showfile?