It's not normal behavior for MC. That's why I think something got messed up on your system. My suggestion was something that was suggested in another post on this subject a while back - and seemed to work for that person (tip - use the Search button).
I assume the file is in your Library now. That is why I suggested re-importing it. Maybe the first time you added it the path got messed up. If it is not in your Library, where is it?
To test playing movies outsdie the Library, I just popped in a DVD disk and selected one of the VOB files (from Windows Exlporer) and it opened and played fine. So I don't think there is a bug in MC.
In the MC settings (Tools>Options>File Types do you have the "File Association" box "checked" for DVD Video (vob, ifo) files? Do you have the Playback method set to Automatic or something else?