At the moment the com.fasterxml.jackson.datatype.joda.ser.DateTimeSerializer writes the following code if the WRITE_DATES_AS_TIMESTAMPS feature is disabled:
...
jgen.writeString(value.toString());
...
whereas value is the DateTime object. However this doesn't take the configured timezone into account which might be set in ObjectMapper.setTimeZone(TimeZone timeZone).
A similar Issue was fixed for the DateTimeDeserializer see: #14