Clicks on drop down option lists that are outside the normal bounds of a dialog box bleed through to the background. I regularly encounter this problem when managing the Advanced Loot window at the same time that I'm tanking. I'm changing the current setting within the bottom-most "Set All To" dropdown list to another option, and my selection click also causes my target to change. I would very much prefer my target to NOT change while clicking a menu item.
I had this screen shot copy-pasted in my first post, but it didn't post the image. So that's a forum bug. Then I go to edit my post to add the image, and the edit box is completely blank, making editing impossible. So that's another forum bug. Let's see if the screen shot posts this time.