Mixin not working correct in Rails 3.2

[noctivityinc]

I've been using FB for years, mostly in Rails 2.3 apps. Im upgrading an app to 3.2 and Im finding that FB is not working. The normal button state appears to be white with the actual desired button state only appearing on hover.

For example, I have this in my Sass file:

a.button
        +fancy-button(#57b42c)
        width: 100px

but when it renders it is white. If I inspect the element and turn OFF the background-image property that references button_bg.png then it works correctly.

I've checked and I have button_bg.png in the images folder and it is resolving in my tests.

Not sure what to do at this point to get this to work other than forking and removing the call to button_bg.png, which seems odd.