[rules-users] Drools Fusion: expiration

Hi all, i have noticed a strange behavior, but i am not sure that i depend on drools or depend by my bad knowledge of it. I am using drools fusion and i have a lot of classes with role event. I have put them the expiration value to 5 minutes. 5 minutes and that event is out of scope of all my rules, that event is deleted. But, i noticed that the last event hasn't retracted after 5 minutes and this behavior makes the system no stable, because it works differently after some minutes. If i don't use explicit expiration, the system seems to work fine, so i am however happy, but i would like to understand the issue. Thanks a lot, Matteo.