Extra entry in the alarm log when alarm is acknowledged

We are using legacy alarm storage in Version 7.6.4. We are finding that if an alarm clears when it is acknowledged we get an extra entry in the alert_log with active, cleared and acknowledged time stamps all identical. If the alarm clears without acknowledge or if the alarms clears later after the acknowledge then only one entry appears in the alarm log.
Our standard PLC code will retain the alarm as active until it is both acknowledged and the alarm condition is no longer present so this occurs quite frequently.