I'm trying to use a converter in HtmlLayout but it was not logged correctly. I'm basically getting a "PARSER_ERRER".

I checked the code and found

HTMLLayoutBase.start() does this.head = p.compile(t, getDefaultConverterMap());

where
protected Map<String, String> getDefaultConverterMap()

{ return PatternLayout.defaultConverterMap; }

But PatternLayoutBase.start() does this.head = p.compile(t, getEffectiveConverterMap());
and getEffectiveConverterMap loads the extra converters.

This is probably in issue in other Appenders too. Maybe the solution can be generified to make it work for every appender?