Relates to:
Somehow I had overlooked the prudent property completely. One more clarification, please: logback.qos.ch/manual/appenders.html#prudentWithRolling states that the file property must be left empty. How do I specify the log file in this case?

See also http://stackoverflow.com/questions/3980934/logback-stops-logging-after-configuration-reload/4008509#4008509