> I was wondering if anyone knew the cause of the problem I am
> experiencing, and a solution--as opposed to a workaround.
It's not a workaround. When you reframed and resized your HDV footage to fit into an NTSC frame size, all those settings were retained, so copying the clips back to an HDV frame size did not make a difference. No experienced editor will try to change the edits in a timeline that was intended strictly as a middle step for one single, temporary output.
If you really insist on keeping the clips that had been modified for the NTSC timeline, then paste them back into an HDV timeline, select the clips and press OPTION-APPLE-V (Remove Attributes) to remove the scaling and repositioning on the clips. However, that's a very silly and unnecessary way to approach this, because any resizing or repositioning that was an intentional part of the edit will be removed as well.
Next time you do this, don't make edit changes to the NTSC timeline, and don't copy the actual clips (edits) over. Either export a movie file of the HDV timeline and import that into an NTSC timeline, or nest the sequence into an NTSC timeline. You can resize/reposition that for output purposes, and then ditch the NTSC timeline when it's time to go back to editing.
Whoever's teaching you guys Final Cut Pro at your school should explain how to do this stuff rather than let you guys feel your way around on your own. It's not very responsible teaching.