To reproduce, create a simple app such as:

object Main extends App {

  val x = readInt()
  val y = readInt()
  println(x + y)
}

When run and supply numbers (1, 2) you get the following unexpected error:

[E] Exception in thread "main" java.lang.NumberFormatException: For input string: "2"
[E] at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)

The same does not occur if running with sbt.

(p.s. Loving Bloop)