uialertview not opening as the top window

I'm opening an UIAlertView which works fine on the iPhone, but when running on iPad 3.2, the alert doesn't come to the top:

UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"" ...];
[alert show];

It's as though it's hidden beneath whatever UIView is currently at the top. If you've encountered t开发者_StackOverflow社区his before or can suggest a solution (window ordering, visibility, moving view placements, etc) that would be most appreciated.