I've been using the low fees of the last few days to move some balances into new segwit addresses. I'm using 0.96.3.992 on Ubuntu 16.04 for both online and offline.

Usually the offline signer confirms that receiving address is indeed in one of my wallets, but this last time it didn't, just listing the 3... destination address. I thought this unusual. I haven't yet figured out how to get the offline to list the wallet segwit addresses ("preferred receive address type" has P2SH-P2WPKH greyed out) so I started up my mirror online machine (not great practice I know, but I like to have one working machine during upgrade procedures). On this "machine B", which is as far as I know identical to the "machine A" that generated the transaction, and has up to now has shown the same many transactions and addresses, the wallet's unused segwit addresses are completely different! I abandoned that tx. A test tx generated on machine B did have the offline machine recognise the segwit receiving address.

I'm worried that somehow machine A has had its receiving addresses replaced by external ones to which I do not have the keys. Surely this isn't possible?

Obviously I can delete and rebuild online machine A, but should I look into this further?