I fixed this manually by adding a media query to the CSS file:
Go to plugins, edit the DiggDigg plugin, and edit diggdigg-style.css, by wrapping all the CSS in a statement like this:
@media only screen and (min-device-width: 480px) {
/* the existing CSS goes inside the brackets */
}
It’s not really about iOS so much as screen size.
I hope that helps…