Queue - Call delivery problems - Asterisk 1.4 - autofill=yes

In Asterisk 1.4 - Using Queue Application
I have configured autofill=yes

I have 2 agents, agent1 is answering a call and agent2 is available.
Sometimes if I have calls waiting, only when agent1 hangup, the queue deliver a call to agent2.

With 3 registered agents it doesn´t happend.

Any Ideas??

Nobody have an idea??