First of all, Thank you!
What I think happend is the following.
OP created a backup in January and kept using the wallet. The wallet kept refilling the keypool whenever needed, but these are not part of the January backup. Sometime in September the 101th key since the backup in Jan was used as a change address. When the wallet was restored from backup. It recognized the transaction because it had one of the keys that controlled the input that was used. Since it did not recognize any of the output addresses it marked them as external and thus is showing them in the overview, whereas it would not show a change output.
I understand, you mean the
transaction was made before the computer crash (that had a return address unknown to the January backup) and the restored backup doesn't recognize the address, hence marks it as outgoing.
(Any new keys generated in the keypool after the January backup are obviously lost.)
I interpreted the post such that the
transaction was made with the wallet restored from the January backup . In this case (if the wallet has caught up with the ledger far enough to determine that all the old 100 keys have been used) the wallet would generate new addresses, right?