Hi,
This is normal behavior (sort of). It really does not matter which IP address appears in CUCM for the CTI RP. When CUCM gets a call for that RP, it sends the JTAPI messages to both UCCX servers as the trigger is associated to both CTI users. The server that is Engine master, responds and continues the call.
Sometimes, if RPs are reporting registered by the UCCX primary in CUCM, something will happen and it will report as registered by the secondary. This 'something' is not known, I looked into it once but after three weeks of waiting and checking every day finally gave up, as it is a cosmetic issue in CUCM and it will not affect call routing.