java ArrayList源码中注释的疑问

Question

 public ArrayList(Collection<? extends E> c) {

elementData = c.toArray();

size = elementData.length;

// c.toArray might (incorrectly) not return Object[] (see 6260652)

if (elementData.getClass() != Object[].class)

    elementData = Arrays.copyOf(elementData, size, Object[].class);

}

c.toArray might not return Object[] 不明白toArray为何会不返回object[]，有没有其他例子说明下呢？ stackoverflow有这个问题，不过回答貌似也没有启发的感觉，是我智商捉急了么- -||http://stackoverflow.com/questions/8521147/why-need-to-convert-type-to-object-array-in-arraylists-construction