As a preamble, you should know that I don't let iTunes "manage" my files. All my video files/folders are on a separate drive.
Here's how I solved the problem of mass tagging mp4 files in iTunes 11 +
1) I Changed the "date last modified" on all video files so they are all the same date, using the program: "Attribute changer" - which allows changing parameters across folders
2) I deleted all the video entries in iTunes (this doesn't delete files, since files are not managed by iTunes)
3) I reimported all the videos, so they all have the same "date added"
4) After that, I had no problem mass editing tags including setting all my videos to "music videos" (which they mostly are, in my case).
This allows all video files on my iPhone to have correct information. Otherwise, home movies or "movies" are without title, unless purchased
It appears that "same kind" means same "added date" and same "last modified date"