It's the icon itself.
Im using anycut, not better cut, but it's the same thing basically. I've used the Aero pack, but I didn't like most of the icons. I've noticed that it just seems to be the way the icon was made. I am unaware of how to make my own icons, and so far haven't needed/wanted to, but I recommend just downloading another icon pack, or changing that icon.
I'm using the Glaskart icon pack, and I've used the BUUF, iPhone 3G (shush, the icons are awesome) and the Creature icon pack as well as the Mario one and I've found that its just a few icons that give me problems in a few of the icon packs I uninstalled.