Since 1.4.0 version of Debugger plugin it stopped printing xml traffic. It only prints interpreted traffic when appropriate system property is set to true. In Openfire 3.9.3 and plugin version 1.3.0 it prints xml traffic by default.
Pull request https://github.com/igniterealtime/Openfire/pull/603 should fix this - let me know if there are any issues.
I think this issue can be closed now the pull request has been merged ...
It looks like it was merged before 4.0.3 release, so it is probably already in the current version. Will mark it as fixed for 4.0.4 so it will go into changelog (can't put in into 4.0.3 changelog now without regenerating it).