I was searching through some old transactions and found that this has happened several times before.
here is my bitcoin.conf file: (with security adjustments)
rpcuser="my_username"
rpcpassword="my_password"
dbcache=5000
#default = 25
keypool=500
#default = 100
addnode=12.47.47.47
addnode=12.229.228.146
addnode=18.215.0.96
addnode=23.21.225.111
addnode=23.23.68.110
The only other settings I've changed are to connect through Tor.
Edit: Just sent a small transaction to try and reproduce the problem but the change went to a new address instead of the old one. Is it possible that keeping the wallets were this is happening in cold storage and not backing them up after every transaction could have something to do with the odd behavior?
