Canvas 当画布元素与另一个div重叠时（Safari 5.1/Mac 10.7.1）

我英语说得不太好。 我开发基于html5的web应用程序。 我已经测试过safari、chrome和firefox。 在safari 5.0之前都没有问题。 但升级safari 5.1后，只有safari 5.1、Mac 10.7.1出现此问题

当画布元素与另一个div重叠时，会出现此问题

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红色的div有黄色的div作为孩子。如果红色div移动，则预期移动黄色div。 但不要移动黄色div only safari 5.1 mac 10.7.1。 当画布区域和子div重叠时会出现此问题。 不发生，不重叠，不执行“canvas.getContext（'2d'）”

这只是野生动物园的臭虫吗？ 有解决办法吗

多谢各位

var d = document.createElement ("div");
document.body.appendChild ( d );

var canvas = document.createElement ("canvas");
canvas.style.backgroundColor = "pink";
canvas.style.position = "absolute";
canvas.style.left = "0px";
canvas.style.top = "0px";
canvas.style.width = "100px";
canvas.style.height = "100px";
d.appendChild ( canvas );
var c2d = canvas.getContext("2d");

var d1 = document.createElement ("div");
d.appendChild ( d1 );
d1.style.left = "50px";
d1.style.top = "50px";
d1.style.width = "500px";
d1.style.height = "100px";
d1.style.position = "absolute";
d1.style.overflow = "hidden";
d1.style.backgroundColor = "gray";

var red = document.createElement ("div");
d1.appendChild ( red );
red.style.position = "absolute";
red.style.left = "10px";
red.style.top = "10px";
red.style.width = "100px";
red.style.height = "100px";
red.style.display = "none";
red.style.backgroundColor = "red";

var yellow = document.createElement ("div");
red.appendChild ( yellow );
yellow.style.position = "absolute";
yellow.style.left = "10px";
yellow.style.top = "10px";
yellow.style.width = "50px";
yellow.style.height = "50px";
yellow.style.backgroundColor = "yellow";


var but = document.createElement ("div");
d.appendChild ( but );
but.style.position = "absolute";
but.style.left = "200px";
but.style.top = "10px";
but.style.width = "100px";
but.style.height = "30px";
but.style.backgroundColor = "black";
but.innerHTML = "Click";
but.style.color = "white";

var flag = true ;
but.onmousedown = function ()
{
    var gap = 5 ;
    red.x = 10 ;
    red.style.display = "block";
    var fn = function ()
    {
        red.style.left = (red.x+gap)+"px";
        red.x += gap ; 

        flag = !flag ;
        if ( red.x > 1000 ) return ;
        setTimeout( fn, 10 );
    }

    setTimeout( fn, 10 );

}