maptalks's version and what browser you use?

"maptalks": "^1.0.0-rc.37",
"maptalks-gl": "^0.99.2",

Issue description

使用 PointLayer 加载 Marker 时，文字始终存在于所有图标顶层
http://examples.maptalks.com/examples/raw/cn/vector/pointlayer/mouse-highlight
官方例子中缩小地图，当图标聚合在一起时此 bug 复现