[R] panel.xyplot : incorrectly "connecting" points

[Greg Tarpinian]

R 2.2, WinXP.  I am having problems getting the right kind of
xyplot( ) to be generated.  The first of these works fine, but
doesn't overlay a reference grid (which I need):

xyplot(Y ~ X | Factor1, type = 'b', groups = GROUP, 
col = c(1,13), pch = c(16,6), lty = 1, lwd = 2, 
cex = 1.2, data = FOO.Frame, 
between = list(x = .5, y = .5),
scales = list(alternating = TRUE))



The second of these displays the grid as I need, but incorrectly
"connects" the points from _different_ GROUP values within each
panel.  I have made sure that GROUP is an ordered factor:

xyplot(PROB ~ MEAN | SD, data = SimProb,
groups = GROUP,							
between = list(x = .5, y = .5),
scales = list(alternating = TRUE),
panel = function(x, y, ...)
   {
    panel.grid(h=-1, v=-1, lwd = 1)
    panel.xyplot(x, y, type = 'b', col = 1,
                 lwd = 2, cex = 1.2, ...)
   }
   )
           			

I am sure that this sort of question has been asked before, and
I apologize for any redundancy.  I would appreciate any help.

Kind regards,

     Greg