Overloaded implicits

Does anyone know of a problem with overloaded implicit methods ? Here's a gist with an example that doesn't compile (https://gist.github.com/1525066). I also pasted it below in case you cannot open the gist:

package bmrk.eod.parsing.examples.inference

import java.util.SortedMap




object Implicits {

  implicit def implicitDef[T <: AnyRef](key:String,columns:SortedMap[String,String]) (implicit m:Manifest[T]):T = {

    null.asInstanceOf[T]

  }




  // If the next method is removed this file will compile

  implicit def implicitDef[T <: AnyRef](key:String,columns:List[(String,String)]) (implicit m:Manifest[T]): T = {

    null.asInstanceOf[T]

  }

}




class Test {

  import Implicits._




  def someMethod[S](implicit anotherMethod:(String,SortedMap[String,String]) => (Manifest[S]) => S) = {

    anotherMethod(null, null)

  }




  val foo = someMethod[String]

}