Save the last activeObject and delete clipTo if activeObject !== lastActive.
var obj = canvas.getActiveObject();
if (!obj) return;
if (lastActive && lastActive !== obj) {
lastActive.clipTo = null;
}
var roundness = Math.round(Math.random() * 60, 2)
obj.clipTo = function (ctx) {
ctx.arc(0, 0, roundness, 0, Math.PI * 2, true);
}
lastActive = obj;
canvas.renderAll();
Look here: http://jsfiddle.net/Kienz/qfgfj/