when you send funds from your Bitradio wallet, the specified amount of funds are sent to the intended Bitradio address and the remainder of the funds being stored in the sending Bitradio address are sent to what is referred to as a "change" Bitradio address associated with the same Bitradio wallet.
Consider the example of taking a $20 bill out of your wallet to pay for a $5 cup of coffee. You would give the $20 to the cashier, and the cashier would give you back the $15. While the $15 belongs to you, it is not available for the time it takes the cashier to give you back your change.
Please see the following Bitcoin Wiki article regarding how change addresses work:
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