Why does UITextField begin editing when view controller is popped off the navigation stack?

Question

I have a single UINavigationController, with an arbitrary root view controller. Then, I push the following subclassed UITableViewController onto the nav stack:

@interface BugViewController : UITableViewController <UITextFieldDelegate>

@end

@implementation BugViewController

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    return 1;
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    UITableViewCell *cell = [[UITableViewCell alloc] init];

    UITextField *textField = [[UITextField alloc] initWithFrame:CGRectMake(100, 0, 200, 30)];
    [textField setBackgroundColor:[UIColor yellowColor]];
    [textField setDelegate:self];

    [[cell contentView] addSubview:textField];
    return cell;
}

- (void)textFieldDidBeginEditing:(UITextField *)textField
{
    NSLog(@"did begin editing");
}

- (void)textFieldDidEndEditing:(UITextField *)textField
{
    NSLog(@"did end editing");
}

@end

Basically, it's just a stock UITableViewController with a single row, which contains a single UITextField.

Repro steps:

1. Tap the text field
   • "did begin editing" is logged, as expected
2. Tap "< Back" in the nav bar
   • "did end editing" is logged, as expected
   • "did begin editing" and "did end editing" are logged again (unexpected!)

I am struggling to understand why the text field begins then ends editing again during the back animation.

Note that I can prevent this behavior by overriding viewWillDisappear:animated: and calling resignFirstResponder on the text field, but I still don't understand the underlying issue.