Strange IE8 behaviour

Question

Recently published project in beta stage. Was testing it with new browsers for a while.

I fixed all bugs including background-size, some main css3 properties on IE8. The only issue on IE8 is following:

To quickly recreate the situation please enter to the website http://goo.gl/rlmelu and click on, for example, birthday. Then enter number of participiants, for example 30 and select some date. Then click "next".

That's how Firefox 26.0, Chrome shows result:

http://joxi.ru/3w7gUv3JTJDfEIXmJqM

And thats how IE8:

http://joxi.ru/Eg_gUv3JTJB-EJupfnA

Please don't tell me to not to use IE8.

What am I doing wrong? How to fix it?

Answer 1

First Problem : The Choose Button

The Problem is CSS PIE.

Two possibilities:

Disable PIE
In iefixes.css, disable PIE for .btn

Set to important
Set the Background to important (But think about: Is !important bad for performance?):

.btn-warning{
    background-color: #f0ad4e !important;
}