QTreeWidgetItem check box does not get updated always.

In a certain way of operation, check box of QTreeWiedgetItem does not get updated. Attached example reproduces this:

In the attached example, some check-able tree widget items are added into the tree widget. The check state will become abnormal after the following steps:
1. Launch application.
2. Un-check item "Level 3-1"
3. And then check item "Level 1". (Do not move mouse)

The resulting check state of "Level 2-1" is still unchecked though it should be checked. It will be updated as checked after mouse is over or window is re-sized.

Edited: There is another related issue happens with the same steps. After step 3, only one signal "itemChanged" is sent for the item "Level 3-1". (no the same signal sent for the items "Level 2-1" and "Level 1").