Hi Ken,
The attached property by itself doesn't actually do anything. Our ButtonBase and ComboBox base controls expose that dependency property as a public StaysOpenOnClick property on their respective classes. Then code inside those classes will not blur focus back to the main focus scope when the button is clicked, etc. if StaysOpenOnClick = false. The property really only affects those instances it is set on and isn't inherited.
If you would like to email our support address with a new simple sample project that shows the problem you're having, we can have a look and make some suggestions on how to handle it. In your email, please reference this thread and rename the .zip file extension of whatever you send so it doesn't get spam blocked. Thanks!