Implicit vals in traits behave differently with type annotation
===

Just wondering if the following is a bug or a feature:

    Welcome to Scala version 2.10.0-M3 (Java HotSpot(TM) 64-Bit Server VM, Java 1.7.0).
    Type in expressions to have them evaluated.
    Type :help for more information.
    
    scala> class TypeClass[T]
    defined class TypeClass
    
    scala> trait A[T] {
         |   implicit val t = implicitly[TypeClass[T]]
         | }
    <console>:9: error: could not find implicit value for parameter e: TypeClass[T]
             implicit val t = implicitly[TypeClass[T]]
                                        ^
As expected, this doesn't compile because there's no constraint on `T`. But when I add a type annotation it compiles:
    
    scala> trait A[T] {
         |   implicit val t: TypeClass[T] = implicitly[TypeClass[T]]
         | }
    defined trait A

Shouldn't the compiler be complaining here? Why should a type annotation make a difference? If we instantiate something with this trait, `t` is `null`.