Out of interest, has Microsoft made a KB article with details of the issue that you know of?
I don't know? I have a very simple program that proves the bug. The program has three elements. A text entry box, a button object that opens an external window, and a menu item that opens an external window. You can type in the text box, and open the external window as many times as you wish from the button, but once you open the external window with the menu item, it disables text entry until the program is restarted.
Here is where you can download the test program: HERE