Gist trying to understand if Swift prevents capturing self in an initializer of a value type

SelfCapturePuzzle.swift

// known confusing on Swift 2.1, Xcode 7.1 

import Foundation

public class InnerMutator {
  var f:(() -> Void)?
}

public struct MutableValue
{
  let innerMutator:InnerMutator
  
  var counter:Int = 0
  public mutating func increment() {
    print("ENTRY: increment")
    self.counter = self.counter + 1
    print("EXIT: increment")
  }
  
  init() {
    self.innerMutator = InnerMutator()
    // all of self's properties are now initialized
    self.innerMutator.f = {
      print("ENTRY: closure")
      self.increment()
      print("EXIT: closure")
    }
  }
}

var c = MutableValue()

c.counter  // => 0 as expected
c.increment() // logging indicated increment() is called
c.counter  // => 1 as expected
c.innerMutator.f?() // logging indicated increment() is called
c.counter  // => 1, instead of 2. WWHAT?

/*
What's puzzling here is that increment is being called, but there is no indication
that any instance has been incremented.

Is there a prohibition or a bug relating to capturing self in an initializer?

Or is the capture of self capturing-by-value instead of capturing-by-reference, in
violation of the usual Swift rule that all capturing captures by reference?

*/

c.innerMutator.f = { c.increment() }
c.innerMutator.f?()
c.counter