ComboBox with CheckBoxes in WinForms [closed]

Question

I am trying to implement a CheckBox ComboBox. I followed this link as a reference

http://www.codeproject.com/Articles/31105/A-ComboBox-with-a-CheckedListBox-as-a-Dropdown?msg=4152597#xx4152597xx

But there are some problems with this example.

1) After the drop-down list is shown, the very first mouse single-click to change the selected item's check-status always fails to do so, but succeeding single-clicks are fine. It seems the very first single-click is swallowed. I did some trace works but failed to find an answer.

2) The form loses focus when the list opens.