When is going to FIX the hangup problem?

Hi, i’m running asterisk-1.4.11 and my PBX have a delay of 10 or 11 seconds to hangup the answered line after the client hangup.

I’m using signalling=fxs_ks
Using an analog Meridian Phone system the line hangup inmediatly the clients hangup their phones.
But in asterisk NO!?