SVG color matrix 'bug' in iOS

HTML

<svg xmlns="http://www.w3.org/2000/svg"
                 xmlns:xlink="http://www.w3.org/1999/xlink"
             width="256" height="256">
            <defs>
                <filter id="filter_ok">
                    <feColorMatrix type="matrix" values="0 0 0.22 0 0
                    0.25 0.25 0.25 0 0
                    0 0 0.22 0 0
                    0 0 0 1 0"></feColorMatrix>
                </filter>
                <filter id="filter_wrong">
                    <feColorMatrix type="matrix" values="0 0 0.22 0 0
                    0.25 0.25 0.25 0 0
                    0 0 0.22 0 0
                    -0.5 0 -0.5 1 0"
     />
                </filter>
            </defs>
                 <text filter="url(#filter_ok)" x="10" y="20">This is filtered to be red</text>
                 <text filter="url(#filter_wrong)" x="10" y="50">This is black on iOS safari</text>
        </svg>