Dear Jan,
CWC should be set up with manual-in mode only. In all other scenario's the agent must have the discipline to enter a CWC during the ACDcall. Even then work-code option must be on "forced" in the huntgroup. And moreover, even then it is possible for an agent to fool the system by pressing AUX-button and returning to manual-in without entering a CWC.
Good luck,
tiramisu