Why did my clips flip upside down and change colors in the sequence.

Our school is new to premiere pro.  We are editing news packages.  The kids are using P2 footage that has been ingested into the machine.  Randomly, while working, all the clips in the timeline are displayed upside down.  Some are black and white.  Some that have a lower third graphic look like they have a negative filter on them.  This hasn't happened to students who are using footage from a panasonic avc camera.  All the machines are the same.  Any help would be great.