Photoshop brushes not showing up in Gimp properly?

I created a star brush in Photoshop CS4 today; exported the preset to an .abr and then put it in my GIMP brush folder. The brush was a "varying" brush, if you will, (meaning it changed opacity, jittered and switched perspective a little) and worked fine in PS. When it loaded in GIMP, none of the aforementioned attributes worked! It was just a static brush. Other "varying" download brushes' attributes work but not this one. Can someone please explain how to correct this?