[Asterisk-Users] Hangup's not detected correctly

[Ruben Fagundo]

I have an easy question. I setup Asterisk with a TDM400 w/ 4FXO ports 
and I have the following problem.

A call comes in correctly. The callers dials extension 100 (grandstream 
SIP phone). The caller then hangup, before the call goes to voice mail, 
however, the phone continues to ring, then goes to voicemail, and leaves 
an empty vmail message, long after the caller has hung up.

Is there a way I can correct for this, ie, have the system detect 
hangups correctly ?

Ruben