Dropping a call is a standard ploy in all centres where the agent feels that in continuing the call it might take them over some other stats on which they are monitored (ie length of call time). Most centres systems are not sophisticated enough to detect who dropped the call so I am afraid this is behaviour you will see from time to time.

I know in some areas it is more prevalent at particular times of the week or month ie towards the end of the monitoring period if the agent knows they are on borderline stats