Before/after in fullscreen

Hello,

in the normal development view I can switch between "before" and "after" using Shift-v (using German as language, should be \ in English), I also can see a text "Before" next to the picture when the before-picture is shown.

In fullscreen preview (F) it seems I also can use Shift-v: I get the text "Before" but the picture does not change.

Is this a bug?

Using Win7-x64, problem occured both with LR5.4 and LR5.5.

Thanks,

Tom