Are you importing the voiceover into the voiceover track or soundtrack?
If you add it into the soundtrack option, there is a selection box that you can unselect for it to loop.
If you add the voiceover into the voiceover track, there isn't a way for it too loop. You might have added it to the wrong audio option.
I saw a thread in 2014 that said the software fix was planned however this is still happening to me. How do I stop the voice over i have uploaded from looping? Thanks