After starting X/fvwm2, the desktop fails to scroll/switch
when the mouse is moved to an edge. One has to manually
switch desktops using the pager. From this point on,
automatic scrolling/switching works.
I have verified this bug to be true. When you first start fvwm you
cannot scroll with mouse from one virtual screen to another until you
click a different window in the pager module. It then scrolls from one
screen to another properly.
That is just the way fvwm2 appears to be working, and from looking in
the source this behavior looks to be intentional. Dunno why.