Yesterday evening I installed the Bitcoin Core wallet (v0.11.2 (64-bit) from the Chocolatey repo to my Windows 10 machine). I had some coins in an old wallet.dat that I copied to the data directory. That worked fine. While the Blockchain was downloading, I transferred the balance from the old wallet to a new address (in my MultiBit HD wallet):
Bitcoin Core wallet created a new transaction to that address in the transaction list. Unfortunately, a few seconds later, it also created a new transaction with the same amount, but to an unfamiliar address:
This new transaction was soon confirmed, while the transaction I entered remains with status Conflicted.
Here's (the relevant part of) the transaction list in Bitcoin Core wallet:
Here's the transaction I asked Bitcoin Core wallet to create, and the mystery transaction it created on it's own initiative:
What could have happened here? Is there any way I can find the PK for the mystery address (could it be a change address in the wallet or something like that)?