Run DragablzDemo.net45 on a screen running at a DPI higher than 100% (96dpi). The issue is more evident if you have two monitors and move the window to a monitor to the right so the coordinates involved are larger.
Maximize the "Simple form of bound tabs" window.
Click and drag down in the title bar of the maximized window to trigger a Restore and the window will either disappear or be positioned incorrectly. The window can disappear b/c it's Top,Left coordinates are off-screen.
To repro: