Duplicates show immediately after originals
I am learning vocabulary words, and after several repetitions duplicate the word and switch the Q&A around to learn the word pair in the opposite direction. However, SM 15 (and now 16) schedules these pairs right after each other. That gives a false positive on that review, as I know the word only by virtue of having reviewed the opposite word pair in the prior repetition. What can I do about this problem?
This is a problem only early in the process and in small collections. You can always randomize repetitions or manually reschedule similar items while creating them. However, the simplest and cheapest solution is to never worry about it. SuperMemo will sort it out assuming no exam deadlines. If you know the answer only because of having a similar item minutes before, you can (a) reschedule the question with Ctrl+J, or (b) provide a what-would-be grade (e.g. fail). You will never escape interference (from outside world or SuperMemo itself).