I'm new to Scala, and I'm struggling to understand why I sometimes don't get a type error when supplying the wrong argument to Set.contains

Here's a quick example using the REPL (2.9.1.final):

scala> val baz = Map("one" -> 1, "two" -> 2)
baz: scala.collection.immutable.Map[java.lang.String,Int] = Map(one -> 1, two -> 2)

scala> baz.values.toSet.contains("asdf")
res3: Boolean = false

Why didn't I get a type mismatch there?

If I assign baz.values.toSet to another val, and call contains on that, I do get type checking:

scala> val bling = baz.values.toSet
bling: scala.collection.immutable.Set[Int] = Set(1, 2)

scala> bling.contains("asdf")
<console>:10: error: type mismatch;
 found   : java.lang.String("asdf")
 required: Int
              bling.contains("asdf")
                             ^

Stupid mistake, language subtlety, or compiler bug?

scala type-conversion
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