Update: Klite didn't have the HAALI Spitter that I could see so I uninstalled it again and rolled back. I then installed the HAALI Splitter (named the Matroska Splitter), from here
https://haali.su/mkv/ and installed it. During the install, I deselected all options part from MP4.
Picasa now sees MP4s and my other video programs don't appear to have been messed up.
Thanks, Bushfiva!