title: observer is not receiving messages for keyPath in KVO
body: <p>I have an object <code>data</code> of class <code>EquationData</code>. I also have a custom tableviewcell (balanceCell), which has as a subview a custom text field (balanceCell.leftView). The text field has a property of type NSMutableString <code>equationOrder</code> which changes as the user types in text. I want <code>data</code> to receive notifications as more objects are added to <code>equationOrder</code>.</p>
  
  <p>What I have in the view controller</p>
  
  <pre><code>- (UITableViewCell *) tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
  
  
      equationCell = (EquationCell *) [tableView dequeueReusableCellWithIdentifier:@"equationCell"];
  
      if (equationCell == nil) {   
          NSArray *nib =   [[NSBundle mainBundle] loadNibNamed:@"EquationCell" owner:self options:nil];
          equationCell = (EquationCell*) [nib objectAtIndex:0];
  
         [equationCell.leftView addObserver:data forKeyPath:@"equationOrder" options:NSKeyValueObservingOptionNew context:nil];
      }
  
      return equationCell;
  }
  </code></pre>
  
  <p>What I have in data's implementation</p>
  
  <pre><code>- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
  {
  if ([keyPath isEqualToString:@"equationOrder"]) 
  NSLog(@"called");
  
  }
  </code></pre>
  
  <p>However, "called" is not displayed on the screen. I have tried using other variables for <code>data</code> to observe, and I've tried changing <code>equationOrder</code> from a property to just a variable. </p>
  
  <p>How do I get <code>data</code> to receive notifications as <code>equationOrder</code> is changed? (I've made sure that objects are actually added to equationOrder)</p>