I had multiple duplicate lines for both interest and dividend income from a single institution on the smart worksheet for schedule B. The worksheet also was missing other data that should have been reported for that same institution. Result was under reporting income and IRS sent me a notice.
if you import twice, or you enter manually and import, you will have duplicates. That's all there is to it.
It is your responsibility to review the entire return for accuracy before you file it ... duplication of entries is one you should catch easily and correct before you efile the return.
yes even if you import just once, Turbotax has been known to mess it up.