Version: 1.4 (using KDE 4.4.0) OS: Linux Installed from: openSUSE RPMs the video thumbnails in the information tool box are always generated by the mplayerthumbs plugin even though it is disabled in the configuration dialog (kffmpegthumbnailer is enabled). the thumbnails in the main view are generated correctly. after deleting the mplayerthumbs' .so and .desktop file is works as expected.
@Daniel: how did you enable kffmpegthumbnailer?
dolphin -> settings -> configure dolphin -> general -> previews -> check: Video Files (kffmpegthumbnailer) and uncheck: Video Files (mplayerthumbs)
Created attachment 49837 [details] shows the video preview before and after removing the mplayerthumbs plugin i installed kde 4.4.4 today and made a screenshot of the bug. then i removed the videopreview.so and .desktop files and now it behaves as expected.
Closing, works for OP :)