I've opened a TAC Case regarding this, but I figured posting this one here as well couldn't hurt.
Here's the scenario, and note it affects inbound calls from the PSTN via the SIP Gateway to CUCM to the UCCX as well as CUCM phone to phone calls.
Called into my test ACD phone from another CUCM phone and answered using the ACD. The call answered, and for exactly 1 minute the CAD was un-responsive. I regain call control. Attempt to put the call on hold using the HOLD button. I click it, the call HOLDS then immediately UNHOLDS and the CAD again goes unresponsive, this time for closer to 30 seconds. I then again put the call on HOLD, it HOLDS now correctly, but the CAD locks for 10 seconds, I take the call off HOLD and I again can speak to the other phone.
I click TRANSFER and get the Transfer a call keypad. I select a number from the list (my Cel Phone) and double click it. The Transfer A Call window locks up for the duration of the call. I can control the call via the phone to complete the transfer, but the Window doesn't close until almost 30 seconds after the call was released to the switch.
I have not attempted Conference as I feel little confidence this would be successful.
The same is repeatable to any call sent to the CSQ and answered normally.
12 Agents + 2 Supervisors
Win7, Vista, and some XP
All agents can log in successfully, and can continue to take calls as they are presented to the phone. They can also hold, transfer, etc via the phone. It's only the CAD that's affected.