parens vs. braces

braces.scala

scala> case class Foo(x: Int = -12345)
defined class Foo

scala> def y = 5
y: Int

scala> val x = Foo(y)
x: Foo = Foo(5)

scala> val x = Foo{y}
x: Foo = Foo(5)

scala> val x = new Foo(y)
x: Foo = Foo(5)

scala> val x = new Foo{y}
x: Foo = Foo(-12345)

scala> x.getClass
res0: Class[_ <: Foo] = class $anon$1

http://scalapuzzlers.com/#pzzlr-036

and

https://gitter.im/scala/scala?at=55a86b33ad99869443daa070

which constitutes a trend.