UITextField not responding to onscreen keyboard presses?

I've got a really weird problem whereby I when I click on a UITextField the ons开发者_JAVA百科creen keyboard pops up, and I can delete characters in the text field - but I cannot type into it!

Background info:

I'm placing the UITextField into a UITableViewCell, which in turn is being got from a table that is being placed into a UIAlertView. I still have the same problem if I place the UITextField directly into the UIAlertView using the UIView addSubview: method.

I have managed to write a UIAlertView in the past that has a UITextField within it working correctly.

Any help or suggestions would be much appreciated - thanks!

Answer can be found in comments under the question.