UIButton's background-inset attribute is ignored

[andreacremaschi]

Hi,

I just begun to use Freestyle and I love it!
As I understand the documentation, background-inset should allow to use stretchable images as UIButton's background with cap insets, am I right? I am using this SASS style snippet but as a result I get a wrong stretched background image (i.e. cap insets are ignored). Am I doing something wrong?

button.confirm {
    color: $white;
    background-image: url(menu_button_green.png);
    background-inset: 2px 28px 3px 34px;
}