I have to split this answer into two parts:
I’ve fixed the bug that caused the missing movie extensions, the new beta is just uploading.
I’ve also added a button to reset the file type definitions to their default values.
It seems as if something has changed in the WIA subsystem with Windows 7, which causes the videos not to show up. ATM, I’ve no idea what it is, and how to fix it, sorry. I’m in contact with another programmer who is experiencing the same problems, maybe one of us will find a solution some day, but until then, a flash card reader or something like that is the only way to be sure that all files are shown.