Anchor is not set to undefined on property binding

Here I have an element that will alternate its alignment inside the parent once you click it. It will start aligned to right, then if you click, it will align to left, and switch back again on the next click.

The working-example.qml shows this test case working. I'm using AnchorChanges and alternating states. The next file bug.qml shows the same case but using property binding instead. I set to undefined if I don't want to align on that corner. The problem is once you click the first time, the element is indeed aligned to left, which is ok, but if you click again, then the square element become a rectangle that is anchored to both parent's left and right.