base64 woff font in dashicons.css causes wp-admin doesn't work

Hello.

We recently upgraded to WordPress 3.9.1 and the admin panel doesn’t show correctly because the dashicons.css uses a url with a base64 encoded file.

It makes the url very long and we see in the load-styles.php source code in the browser:

@font-face{font-family:dashicons;src:url(">'>
Syntax error in document. <br>
Can't rewrite url because it is too large. <br>
Transformation aborted. <br>
data:application/x-font-woff;charset=utf-8;base64,d09GRgABAAAAAFc4AA4AAAAAjggAA...

Why is WP using this? Is it possible to use simply this?

@font-face {
font-family: "dashicons";
src: url(../fonts/dashicons.woff) format('woff'),

We have changed the dashicons.css and dashicons.min.css, but we don’t like to change WP core.

Is there any workaround?

Thank you.