I have tried everything I can think of a failed.

I want to export a rectangle with rounded corners with a colour fill linear gradient.

This is to create a background url for a button which which need to emulate standards compliant CSS in Internet Explorer.

I am sure many many people have to do this IE hack.

But what ever I do the background under the rounded corners shows up as white space which is no good.

I have:

Made sure the image is sized to the nearest whole pixel.
Made sure it is snapped to grid with whole pixel positioning
Made sure I have set clipview on.
Made sure I have transparent background set.

I have tried the export as a PNG, GIF, JPG and SVG.

None work.

Is this possible or am I wasting my time?