presentViewController:animated:completion wont Animate

presentViewController:animated:completion wont Animate

this is my first question so please go easy!!
I have an iOS app that has 5 tab bars, each of which contains a Navigation
controller. It seems that no matter where I call
presentViewController:animated:completion from, I get no animation from
the transition, the presented view controller just appears on screen!
This is also happening with my UIImagePickerController that I am
presenting from one of my tabs. No presenting animation, but when i
dismiss it it DOES animate away!
Here is a sample of the code, sent from a code generated tab bar button,
with its action hooked up to a method which simply does this..
UserRegistrationViewController *userRegistration =
[[UserRegistrationViewController alloc] init];
userRegistration.modalTransitionStyle = UIModalTransitionStyleCrossDissolve;
[self presentViewController:userRegistration animated:YES completion:nil];
If anyone has ANY ideas of things that I could try I would be most grateful!