CSS broken on IE 11, works and all other browsers

Hello,

On our staging server, a hover effect ist broken in IE 11 only:

http://tinyurl.com/j977wsd

If you hover one of the square blue buttons, the flyout CSS is corrupted and the row of blue buttons moves down, which it shouldn't. You can use any other non-IE browser including Edge to see what it should look like.

I would need to know how to fix an issue of this order, since I cannot write IE11 specific CSS. So by fixing IE, I will break all other browsers.

Thanks in advance,

Paddelboot