title: inconsistency between different ways of appending to a slice
body: <p>I came across this inconsistency in calling &quot;append&quot; using variadic form vs appending a single element. See: <a href="https://play.golang.org/p/rR0su5FxhMX" rel="nofollow noreferrer">https://play.golang.org/p/rR0su5FxhMX</a></p>
  <p>Two slices, initialized from same slice.</p>
  <ul>
  <li>Add an element to one of them.</li>
  <li>Add two elements to the other. Scenario 1: add those two elements by calling &quot;append&quot; twice. Scenario 2: add those two elements in a single call.</li>
  </ul>
  <p>Result: In Scenario 1, appending to the second slice overrides the last element of the first slice. Scenario 2 leaves it intact.</p>
  <p>If &quot;append&quot; changes the underlying structure (which should be the case), that explains Scenario 1. Why does it not work the same in Scenario 2? (or the other way around)</p>