Bug while loading/unloading plugins:
Method PluginMonitor.run() (private class in openfire/container/PluginManager.java ) converts the filename of a *.jar file to lowercase. Later when deleting the plugin again this lowercase name is used to delete the *.jar file. This doesn’t work on systems where filenames are case sensitive, e.g. Linux/Unix.
String pluginName = jarFile.getName().substring(0, jarFile.getName().length() - 4).toLowerCase();
This bug includes for example the PacketFilter plugin, see bug report there.
Openfire 3.4.1 (checked source code only)
Convert the plugins *.jar file to lowercase your self and delete the plugin via admin console. Another way is to delete the *.jar file manually. Both works while Openfire is running, too.
Low, since an easy workaround is available.