The option isn't enabled on wizard-created Character Sets for WoW because it isn't required. The setting itself makes any game window that is not in focus think it's in the foreground so that keystrokes can be sent to it, because some games don't accept keystrokes when they're in the background—WoW is not one of those games.
Since others who do use the default setup (i.e. "Make foreground..." isn't enabled) aren't experiencing the issue you describe, it's unlikely going to change anything. As others have stated, you are the one and only person I've heard report this issue at this time.
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