An error occurs while TinyMCE is loaded. Because of this, the standard TinyMCE image upload dialog is displayed instead of the Lenya one. editor_plugin.js, line 18: tinyMCE.importPluginLanguagePack('simplebrowser', 'en'); TinyMCE version: 3.2.3.1
See also http://drupal.org/node/215580
This is IMO due to the fact, that our tinyMCE plugin is incompatible with the 3.x versions of tinyMCE
OK, this is not a bug.