The synchronization target of NTP client does not change for a long time

Issue

• There are RHEL6.2 NTP server and client. They are synchronized from ntpd of the NTP client.
• The following occurred when the NTP server which was synchronized from ntpd of NTP client was stopped.
• The synchronization target of NTP client which was displayed by ntpq command did not change even if a long time (90 minutes or more) had passed since ntpd of the NTP server was stopped.
• Could you tell us the cause that the synchronization target of NTP client does not change for a long time when the NTP server stops?
• Could you tell us what data needs to be gathered to investigate the cause?