Why this erasure warning with member variables declared as a tuple?

Have a look at this Scala class:

class Example {
  val (x, y): (Int, Int) = (1, 2)
}

Compiling this results in a warning:

Example.scala:2: warning: non variable type-argument Int in type pattern
               (Int, Int) is unchecked since it is eliminated by erasure
    val (x, y): (Int, Int) = (1, 2)
                ^

Removing the explicit type annotation gets rid of this warning:

class Example {
  val (x, y) = (1, 2)
}

Why do I get the warning and why does removing the explicit type annotation get rid of it? As far as I can see nothing really changes, x and y are still of type Int without the type annotation.