Cisco 2911 failing to go on hook when disconnect received

[keithhaugen]

The setup is PSTN -> Nortel -> Cisco, and when the PSTN user hangs up the Cisco port remains seized (even though Cisco debugs indicate it has understood a disconnect occurred). There is no SIP BYE sent and the voice port line remains on. the connection is analog between Nortel and Cisco, and all 6 FXO ports on the Cisco box exhibit the same behavior.