Will it duplicate? Probably.
"Sometimes" I've noted that a re-import doesn't duplicate, but only because the forms were really exactly the same. A manually entered form will always be different in subtle ways, and the software cannot know that they are really supposed to be the same form.
You can always delete the duplicate form, but you do have to pay attention to each form's table of what's been entered.
____________*Answers are correct to the best of my knowledge when posted, but should not be considered to be legal or official tax advice.*
