user85611: I did a test lightning transaction by sending 0.00001 btc to some exchange with using bitcoin core 0.16 (downloaded from bitcoin.org and installed to dedicated pc) and... it took the rest balance of my wallet which was sent to unknown address.
Here is the transaction: https://www.blockchain.com/btc/tx/5d6111094be588c180661cb2f0ee21a7de28a7dea8641cb9921b4aada3175dd5
As you can see there is 0.00001 btc sent to some exchange wallet and also 0.00948723 is sent to unknown address (exchange says it's not belongs to them).
What was the second transaction?

user74482: Make sure you are using the latest wallet version.
Try re-indexing your block. Run your wallet with reindex option
bitcoin-qt -reindex
Its clearly a change that should return to your wallet in some time. 
Here your stat - 
Total Input     0.0095 BTC
Total Output    0.00949723 BTC
Fees    0.00000277 BTC


user13866: The second output is most likely change being returned to your wallet. Just like when you use a $5 banknote to buy a $1 item. You get $4 back in change. You don't try to tear off 1/5th of the $5 banknote.
Unspent Transaction outputs (UTXOs) can't be half spent, you spend the whole UTXO and get change back.

85611: <p>I did a test lightning transaction by sending 0.00001 btc to some exchange with using bitcoin core 0.16 (downloaded from bitcoin.org and installed to dedicated pc) and... it took the rest balance of my wallet which was sent to unknown address.</p>

<p>Here is the transaction: <a href="https://www.blockchain.com/btc/tx/5d6111094be588c180661cb2f0ee21a7de28a7dea8641cb9921b4aada3175dd5" rel="nofollow noreferrer">https://www.blockchain.com/btc/tx/5d6111094be588c180661cb2f0ee21a7de28a7dea8641cb9921b4aada3175dd5</a></p>

<p>As you can see there is 0.00001 btc sent to some exchange wallet and also 0.00948723 is sent to unknown address (exchange says it's not belongs to them).</p>

<p>What was the second transaction?</p>
 74482: <p>Make sure you are using the latest wallet version.</p>

<p>Try re-indexing your block. Run your wallet with reindex option</p>

<p><code>bitcoin-qt -reindex</code></p>

<p>Its clearly a change that should return to your wallet in some time. </p>

<p>Here your stat - </p>

<pre><code>Total Input     0.0095 BTC
Total Output    0.00949723 BTC
Fees    0.00000277 BTC
</code></pre>
 13866: <p>The second output is most likely change being returned to your wallet. Just like when you use a $5 banknote to buy a $1 item. You get $4 back in change. You don't try to tear off 1/5th of the $5 banknote.</p>

<p>Unspent Transaction outputs (UTXOs) can't be half spent, you spend the whole UTXO and get change back.</p>
