So this is happening to me too.  I've posted over at the Ledger subreddit (https://www.reddit.com/r/ledgerwallet/comments/701eth/multiple_activations_on_ledger_nano_s_required/), to me it looks exactly like a hack.  We need to get the awareness out there on this as people could just be clicking through on their keys not thinking about it and sending BTC to an unknown address.    Absolutely crazy, if this is a hack then it's disastrous for ledger.  If it's not a hack and it's intended behaviour of the Nano S following the SegWit implementation, then it is still a disaster because it looks like, what else, a bloody hack.  Frankly not sure what possibly resolution there can be to this that is satisfactory - I woke up this morning trusting Ledger with my bags and now that trust is shattered.  Spread the word people, terrifying.