Will be fixed in the next beta.

I noticed the problem with dragging windows in the preview too. My screens are ordered 2,3,1 (left to right) with 3 being the main screen.

Thanks! I see what you mean but now I see I have a different problem! My monitors are arranged with Number 2 on the left hand side and Number 1 on the right. The desktop preview seems to assume I have 1 on the left and 2 on the right. The rest of Dexpot is fine with my arrangement. This is what I see:

If I drag a window on the screen from monitor 1 to monitor 2 (right to left) then the sketch disappears off the preview window to the left hand side. If I drag a window on the preview from left to right, into the blank area where it thinks monitor 2 should be, then the window on screen slides off monitor 1 and disappears.

I can send you a screenshot if it helps to explain but do not know how to incorporate it with this message

Actually, the Desktop Preview is multi-monitor capable, it's just not that obvious. Here's a screenshot of two windows maximized next to each other on two monitors:

I am pleased to see multi-monitor support now but there are two preview functions that do not include the second monitor: Desktop Windows - Preview dialogue and Desktop Preview.