Switching between tree pane and browser pane

[deus-ex]

XnView Classic
My visual setup of XnView Classic looks like this (preview pane permanentely disabled): http://i.imgur.com/Tt1Qpss.png
This way I'm able to switch back and force just between the tree pane and browser pane with the TAB key.

XnView MP
I made a similar visual setup for XnView MP: http://i.imgur.com/6giqp1X.png
Yet I'm unable to switch just between the tree pane and browser pane with the TAB key. XnView MP cycles between the browser pane, the tree pane and a third unvisible item. I cannot make out what this third unvisible item might be and how to disable it. Does anyone have an idea/clue?

[xnview]

right, it's a bug of QT API

[deus-ex]

Which means it is out of your control, i.e. you can't fix it yourself, right?

[xnview]

Which means it is out of your control, i.e. you can't fix it yourself, right?

yes i have contacted the support