Wimp drag clicktypes can trigger erroneously if window size changes

A click in a window that results in the window changing size such that the pointer is now on the furniture causes the Wimp to interpret it as a mouse movement and if the clicktype of the icon or window is a drag type, the Wimp immediately issues another click event with a drag button type, though the mouse hasn’t moved and the dragdelay hasn’t yet passed.

This small basic program illustrates the bug.