Hi, flashkube2,
Failure to import the video portion could be caused by a corrupt preference. Try deleting/resetting preferences.
To delete/reset preferences open iMovie while holding down the Option and Command keys and select to delete preferences in the box that appears. iMovie will open in a new library. Reopen your old library to get back to your projects. Now see if you video-audio clip will import the video part as well as the audio part. Possibly you may need to reboot to set the changes. Deleting preferences is a safe procedure that will not cause data loss or disruption to your project.
You can also try creating a new project and importing your clip into to new project to see if it works there.
-- Rich