Queue wrapuptime issue

We have a queue:

[977] announce-frequency=0 announce-holdtime=no autofill=no eventmemberstatus=no eventwhencalled=no joinempty=no leavewhenempty=no maxlen=0 periodic-announce-frequency=0 queue-callswaiting=silence/1 queue-thereare=silence/1 queue-youarenext=silence/1 retry=0 strategy=ringall timeout=15 weight=0 wrapuptime=20

There is a dynamic agents, who gets a call. wrapuptime=20. But really, when the agent puts down the receiver, the following call incomes only in 3-4 sec. But there should be an interval of 20 sec. What is the problem in?