In scala, How could Map[_,_] and scala.collection.immutable.Map[_,_] have different TypeTag?

They refer to the same thing, yet when I compare 2 type tags:

Map[_, _] did not equal scala.collection.immutable.Map[_,_]
ScalaTestFailureLocation: 
Expected :scala.collection.immutable.Map[_,_]
Actual   :Map[_, _]

How could this happen in a typed language? How do I make them identical?