receiving messages during a drag

[Ben Rubinstein]

I'm trying to accept a drag+drop into a scrolling group.  All fine, except 
that I want to have the group scroll automatically if the user hovers over the 
top or bottom.

If the dragMove shows that the position is at top or bottom of the area, I 
want to scroll the group a bit; then if they're still then a few ticks later, 
scroll it a bit more.

Picking up the dragMove into an appropriate spot is fine; but I then tried to 
send myself a message to scroll a bit more, which I cancel if they move out of 
the zone.  However, it seems that messages aren't sent while a drag is in 
progress - instead the first message isn't sent until the drag ends.  So I 
currently I have something where the user has to wiggle around at the end of 
the group to scroll it - not great!

Is this a known problem?  Is there a way to get periodic operations during a 
drag?

Or do I have to block, once I detect that I'm starting to scroll the group, 
and just poll the mouse position and mousebutton to kep scrolling until the 
mouse moves or the button is released or I'm scrolled all the way?

(And if it is the case that periodic operations are simply stopped during a 
drag; is this a bug?)

TIA,

- Ben