As you might have seen I've created the issue. I also created the pull request. While adding the test I found another bug inside this EventRecordingLogger. In one case the marker got lost.
One of the things I noted while doing this is that the IntelliJ IDEA indent settings for java files is set to 2 spaces, but all code is formatted using 4 spaces. This comes from commit: https://github.com/qos-ch/slf4j/commit/b8b7aaf44d7bb7ecb897ff4327ce8f353d4aeefe. Shouldn't it be changed to "4" for java and only be "2" for XML?