Windows Close (X) button only closes one lister not both

I have a dual lister configuration, I've noticed recently that clicking the Windows Close (X) button now only closes one lister instead of both. I have to click the Close button twice to exit Opus completely. This behaviour only seems to occur if one of the listers is displaying the list of drives attached (My Computer). I think this has only stared occurring since the last update (v11.10). Is this a bug or something peculiar about my set up?

Turn off Preferences / Folder Tabs / Options / Lister close button closes active tab.

That's cured it - Thanks.