Yes I've only ever had the most recent version.
Actually what I've just realised is that it was an earlier transaction which appeared on the block explorer, and also in my client.
I have sent 3 withdrawals to my wallet.
1. Seems to be on new fork (no block explorer to check though) and arrived
2. Seems to be on old fork (shows up in block explorer) and arrived
3. Seems to be on new fork (not in block explorer), never arrived.
Which means Bittrex and my client are hopping forks... this needs sorting. I don't know how many of my coins I actually own, hoping it's at least 2/3rds.