Some wallets offer a change of address service each time funds are received. This service offers you a little more privacy on the network. In fact, the amount of cryptocurrencies stored at a receiving address is information that is accessible to all. Your wallet thus generates a new address folowing the receipt of funds in order to distribute your funds over a tree of addresses which are all dervied from the MasterKey. However, all your previous addresses remain valid and lead to the same wallet.