Error: the type of this expression is underspecified

[sorawee]

Unless I missed something, this program should be verified fine:

method Main () {
  var arr := [[1]];
  var x := |((arr + arr) + (arr + arr))|;
}

but it results in Error: the type of this expression is underspecified.

Subtle changes to the program make it verified:

method Main () {
  var arr := [[1]];
  var x := |(arr + (arr + (arr + arr)))|;
}

or

method Main () {
  var arr := [[1]];
  var x := ((arr + arr) + (arr + arr));
  var y := |x|;
}

EDITED: a more minimal example:

method Main () {
  var x := [1];
  print (x + x) + (x + x);
}

[robin-aws]

I'm calling this a bug since it's really hard for users to explain why type inference fails on this exact expression and not the others.