That makes sense, if you don't understand I will try to explain.Doesnt make sense. It was a old wallet backup. It must work when you start RC4... it did work. It generated a new address in addition after i was using darksend+. Wallets are always backwards compatible. You miss the point. I was using probably 50 different coin wallets that are based on bitcoin and never saw this bahavior. So darksend must be exceeding 100 transactions and generating a new private key in the wallet? I did 8 rounds...
Each coin has a keypool. Lets take your bitcoin wallet as example. You start the client and create a backup. The wallet contains a keypool of 100 pregenerated addresses.
If you recieve coins these addresses are still in your wallet and in the backup.
But as soon as you generate a new address which is not from the keypool or import a private key, you have to create a new backup. Always. This is not new and was there since bitcoin's early days.
Now, what's new with Darkcoin RC4? The keypool was increased to 1000 keys. Now the first launch of RC4 generates 900 new addresses to your wallet. Obviously these addresses are not in your backups, thats why you need to create a new backup. That's no magic, just a huge amount of new addresses added to the key pool.
I'm doing weekly versioned backups of all my active wallets because I know there is a lot of stuff ongoing I might not be aware of. Do regular updates and you are fine, with or without RC4.
And there is nothing to blame, your backups are of course backwards compatible, they just dont include newly generated addresses.