[logback-user] The MDCPropertyMap has been already set for this event Exception

Hi - I have wrote an appender which use `setMDCPropertyMap` to inject some fields to LoggingEvent. It’s fail to working with other build-in appender (e.g. ch.qos.logback.core.FileAppender) Exception: java.lang.IllegalStateException: The MDCPropertyMap has been already set for this event. Regards, Jian