Expression of type Any doesn't conform to expected type_$1
<p>I have problems with undestanding Scala's type system.</p>

<pre><code>class A[T](var value: T)
class B[T](val a: A[T], var newValue: T)

val list = new MutableList[B[_]]()
val a: A[Int] = new A(10)
val b: B[Int] = new B(a, 11)
list += b

val someB = list.head
someB.a.value = someB.newValue
</code></pre>

<p>And after compile i see the error:</p>

<pre><code>Error:(12, 24) type mismatch;
found   : A$A36.this.someB.newValue.type (with underlying type _$1)
required: _$1
someB.a.value = someB.newValue
                      ^
</code></pre>

<p>Both <code>someB.a.value</code> and <code>someB.newValue</code> have the same type but Scala's compiler actually doesn't think so. How this error can be fixed ?</p>