Trigger Resource Problem

Hi All,
I have created one simple model in webMethods6.5 and assigned the following inputs to model trigger:
Queue Capacity: 10
Queue refill level: 4
Maximum Thread: 10
Processing mode: concurrent

And it is running fine but when I have checked trigger resources, it is showing 9 current threads running though there is no document inside the trigger queue.

Do I need to set some setting or did I make some mistake here.

Thanks in advance.