Custom UIButton showing border on iPad

I have four custom UIButtons sitting in front of a UIImageView, but for some reason on the iPad it is showing a white border around them. Essentially开发者_运维问答 it's a UIImageView with a black gradient with four buttons on it. Each button is the height of the image view and they show a white line on each side. Is there a way to get rid of it?

The view was created on whatever XCode 4's version of Interface Builder is called.

I got this when I created the button in code as follows:

[UIButton buttonWithType:UIButtonTypeRoundedRect] 

Which seemed to work fine on iPhone but on iPad I needed as follows:

[UIButton buttonWithType:UIButtonTypeCustom]