Safari on iPhone4S crashes with webkit-backface-visibility

I  removed flickering of an 2400px wide element while animating it by adding -webkit-backface-visibility:hidden; to the CSS. It worked fine. Later on a collegue reported that the Safari of his iPhone4S crashes everytime a section of the page is renderer. I managed to pinpoint the crash to the that line in the CSS. The fix was to replace it with -webkit-transform:translate3d(0,0,0);. No flickering or crashing after that!