On Page 13 of the Rules Reference, it says that during setup:
4. Each player shuffles any number of cards from their hand back into their deck, and then redraws until they have 5 cards in hand.
Rules as Written, it specifically requires you to shuffle the discarded cards back in, and then redraw, which means there's a chance you'll get back the same cards you discarded.
How have you all been playing it?
I would normally assume it was intentional, but my experience with FFG in X-Wing is that sometimes their RAW don't always capture their intent. And this seems kind of counter-intuitive. Normally I would expect one to draw back up to 5, then shuffle the discarded cards in?