Funny __toString() behavior

So here's another behavior in PHP that's not quite what I expected, but not all that surprising.

<?php

class SomeClass {
  public function __toString() {
    return "hello!";
  }
}

class SomeOtherClass {
  public function __toString() {
    return new SomeClass();
  }
}

echo new SomeOtherClass();
?>

Now, doesn't it seem that the echo should carry through to SomeClass::__toString()? You'd think; but you get a fatal error instead. It the "fix" isn't difficult:

class SomeOtherClass {
  public function __toString() {
    return (string)new SomeClass();
  }

And from a performance standpoint, it is better to require a string be returned than try to guess. Seemed odd, though, given PHP's loose typing.