Due to an oversight in the implementation it's possible for function values to have a vararg signature, leading to various kinds of hilarity. Retronym confirms that this is a bug (see tweeties at https://twitter.com/tpolecat/status/392747549733306368)

gistfile1.scala

// Eta-expansion turns A* to Seq[A]

scala> def foo(ns:Int*) = ns.sum
foo: (ns: Int*)Int

scala> foo(1,2,3)
res0: Int = 6

scala> val foov = foo _
foov: Seq[Int] => Int = <function1>

scala> foov(1,3,3)
<console>:10: error: too many arguments for method apply: (v1: Seq[Int])Int in trait Function1
              foov(1,3,3)
                  ^

scala> foov(Seq(1,2,3))
res2: Int = 6


// REPL can't cope with vararg functions

scala> val bar: (Int*) => Int = _.sum
<console>:5: error: type mismatch;
 found   : Int* => Int
 required: Seq[Int] => Int
  lazy val $result = `bar`
                                            ^


// Works if not at top level, but REPL reports the wrong type

scala> object Baz { val qux: (Int*) => Int = _.sum }
defined module Baz

scala> Baz.qux
res0: Seq[Int] => Int = <function1>

scala> Baz.qux(Seq(1,2,3))
<console>:9: error: type mismatch;
 found   : Seq[Int]
 required: Int
              Baz.qux(Seq(1,2,3))
                         ^

scala> Baz.qux(1,2,3)
res2: Int = 6

scala> :t Baz.qux
Seq[Int] => Int

scala> Baz.qux : (Seq[Int] => Int)
<console>:9: error: type mismatch;
 found   : Int* => Int
 required: Seq[Int] => Int
              Baz.qux : (Seq[Int] => Int)
                  ^

// Reassigning a vararg value loses the varargness

scala> val quux = Baz.qux
quux: Seq[Int] => Int = <function1>

scala> quux(1,2,3)
<console>:10: error: too many arguments for method apply: (v1: Seq[Int])Int in trait Function1
              quux(1,2,3)
                  ^

scala> quux(Seq(1,2,3))
res5: Int = 6

scala> quux eq Baz.qux
res6: Boolean = true