Lots of UIButtons slowing things down?

I have an iphone app which has lots of UIButtons (10--90) in the interface.

Recently I have noticed one of t开发者_运维问答he buttons with patches of white as if it not completely drawing. Is it because there are may UIButtons, or something else?

And do lots of UIButtons slow things down?

I have an app with 30 UIButtons that has had no problems in that regard. I'm guessing it's something else. If you really suspect the buttons, you could test by making an app with (say) 100 UIButtons that doesn't do much of anything.