If no Logback appender can be found within the Logback configuration (logback.xml) that initializes the Open-Xchange PatternLayout the custom MDCConverter will not be initialized. This might happen when only the SyslogAppender is used for logging.
To prevent writing PARSER_ERROR instead of MDC the following line must be added to the Logback configuration which will add the Open-Xchange PatternLayouts to the responsible map:
<define name=syslogPatternLayoutActivator class=com.openexchange.logback.extensions.SyslogPa tternLayoutActivator />