Scala Copy() Odd Behavior

I'm experiencing an odd bit of behavior when I use the auto-generated copy() method that was added in Scala-2.8.

From what I've read, when you declare a given class as a case-class, a lot of things are auto-generated for you, one of which is the copy() method. So you can do the following...

case class Number(value: Int)
val m = Number(6)

println(m)                     // prints 6

println( m.copy(value=7) )     // works fine, prints 7

println( m.copy(value=-7) )    // produces:  error: not found: value value

println( m.copy(value=(-7)) )  // works fine, prints -7

I apologize if this question has already been asked, but what is going on here?