MFC CTreeCtrl node (a ComboBox in this case) does not seem to lose focus in Windows 7

Question

My application uses MFC CTreeCtrl. One of the nodes of the tree has a ComboBox control of DropDownList style.

In Windows 7, if we were to select an option from the ComboBox dropdown and then click on another node of the tree, the new node gets highlighted but the focus remains with the CComboBox control! I don't see this behavior on Windows XP.

Doing a SetFocus() (within the OnSelChanged() of the tree class implementation) on the newly selected node helps the new node gain focus but I am trying to figure out why this would work on Windows XP (without SetFocus() being explicitly called) but not on Win 7.

Any thoughts/ideas please?