Moving Icons

Hello Vladimir,

I just discovered your plugin today, it’s very nice, thank you for sharing.
I already built some button into my site and noticed the following issue. If the mouse enters or leaves one of my buttons, the icon moves a little to the left and right. The other buttons on the same site are not affected. You can see this here (the broken button is the first one):
http://www.ornelladesantis.eu/musik/

http://wordpress.org/plugins/shortcodes-ultimate/