SIP Channels not hangup when pickupexten(*8)

Hello everybody.
I have a problem with Asterisk 1.8.6.0 about SIP Channels not hangup when pickupexten(*8).

This console log(core show channel SIP/1908-00014108)

CDR Variables:
level 1: dnid=
level 1: clid=“device” <1908>
level 1: src=1908
level 1: dst=*8
level 1: dcontext=xxxxx
level 1: channel=SIP/1908-00014108
level 1: start=2012-05-25 10:18:38
level 1: answer=2012-05-25 10:18:38
level 1: duration=-667010
level 1: billsec=-667010
level 1: disposition=ANSWERED
level 1: amaflags=DOCUMENTATION
level 1: uniqueid=1337915918.95334
level 1: linkedid=1337915918.95334
level 1: sequence=132483

this called shoule be hangup at 2012-05-25, but the call status still calling.

Have any idea?