Actually, maybe the effect is not clear from my screenshot, the background doesn't just overlap the border of the foreground button, it covers a bigger portion of the button and looks bad when actually animated, it's obvious that there is something wrong rather than just a 1-2 pixel nit pick. It's more like around 10 pixels of the button, so it's probably something wrong going on and not the intended effect as per the example project, which looks good in my opinion.
Also, what does the X Padding do of the uipopuplist? The Y padding works great to separate the elements in the list but the X padding doesn't seem to do anything for me.