LOG4J2-99 I stumbled across another small issue:
When a Log4jLogEvent is reconstructed (in AsynchAppender, MapRewritePolicy or PropertiesRewritePolicy) the ThrowableProxy of the original LogEvent is used to construct the new Log4JLogEvent.
There the ThrowableProxy is proxied again. During this the package resolution is repeated (mostly with slightly different result).
I created a patch for Log4JLogEvent to reuse existing ThrowableProxy objects.