First of all, CUPS 6.0.x does not support OCS 2007 R2. Which means:
1) This combination was not tested by Cisco. Thus unexpected behavior might be observed.
2) If you run into this problem, Cisco (TAC) won't be able to troubleshoot the problem for you (because it's not supported).
You should use CUPS 7.0.x with OCS 2007 R2.
With that said, here are something under the hood:
For MOC RCC, CUPS has to know which phone device to control. CUPS depends on the "device name" in the TEL URI to detemine which device to control.
Before the "phone selector" plug-in was introduced on CUPS 7.0.x, CUPS use a "call-back" method to detect the device. Which is: CUPS will make test calls to the devices that match the DN in the TEL URI. Whoever answered first would be the one choosen. This might be the cause of the "ghost calls".