iPhone: Bug in UITextField component - setTextColor not working

I'm working on a form for an iPhone app that does real-time form validation to let the user know if they're trying to create an account with a username that already exists. To let the user know that a username is already taken, I set the UITextField textColor property to red:

#define kColorRedError [UIColor colorWithRed:1 green:0 blue:0 alpha:1.0]
//... UITextField *username = [[UITextField alloc] initWithFrame:CGRectMake(12, 14, 296, 30)];
[username setTextColor:kColorRedError];

This wouldn't update until I typed another letter into the UITextField, so quite often it would display an error when it shouldn't, and vice versa. I tried using setNeedsDisplay and some other bits of code to try to force a display update after setting the text color. Nothing worked, until I tried this:

[password setTextColor:kColorRedError];
username.text = username.text;

...Quite absurd, but forces a redraw on the component. Gotta love those Apple components ;)