False positive on rgba fallback rule: none and transparent

[jsphstls]

    background: none;
    background: rgba(0, 0, 0, 0.6);

or

    background: transparent;
    background: rgba(0, 0, 0, 0.6);

Both produce:
WARNING: Fallback background-color (hex or RGB) should precede RGBA background-color. For older browsers that don't support RGBA, HSL, or HSLA, provide a fallback color. (fallback-colors) Browsers: IE6,IE7,IE8

If a browser cannot produce a semi-transparent background, you should also be able to remove the background altogether.