Just to set your mind at rest, it's a normal function of the Bitcoin spec which forms the basis for most altcoins.
A Qt wallet contains multiple addresses, which are generated when you create the wallet.
Some of these are used when you 'create' receiving addresses.
When funds are sent to a receiving address, they're not discrete coins. They're just an entry in the ledger (called the blockchain) for a specific amount (say 10 vior)
When you 'spend' some of these coins (say 5 vior) the network changes the ledger entry by removing all 10 vior from your receiving address, crediting 5 to the address that you send to, and returning 5 to another address in Your wallet, known as a 'change address'. This address does not appear in your list of receiving addresses. So as you spend coins, your wallet is accumulating (and spending) the change from each transaction, in addresses that are invisible to the user (unless you use the console).
This is a poorly documented feature, and I don't claim to understand the precise mechanics of it's operation. But these 'invisible' addresses are also available to stake (for a pos coin) although the contents may be trivial compared with the main receiving addresses (so they don't stake very often).
The main thing that you should bear in mind is that if you make a large number of transactions, your wallet can literally run out of addresses (it starts with about 100). In which case it just Generates More to suit it's needs.
But a Backup of your wallet will be unaware of these newly generated addresses in a busy wallet.
So you need to make Regular Backups to remain up to date with newly generated addresses.
Because if you need to rely on a backup (having lost the current version of your wallet) it will NOT contain coins sent to addresses that were Generated after the backup was made. The Balance of the funds from one address is sent to a different address when you spend some. So you can lose funds that you thought were secure even though the Original Receiving Addresses are still in the backup.
So in summary.
There's nothing unusual about these unlabeled addresses. They're a part of the wallet function.
The precise operation of this function varies from coin to coin.
Make regular backups of Any Wallet for Any Coin that's in regular use.
Hope that helps.