Possible bug: polygon and ylimits/vlimits

[Russell Fiedler <fiedler@xxxxxxxxxxxxxxx>]

I'm trying to make a plot of some polygons where the vertical axis is
sigma. Naturally, I would like the polygons corresponding to dense regions
to appear at the bottom of the plot (i.e. the vertical axis needs to be
inverted)

The qualifier /vlimits (and the deprecated /ylimits) appears to be able to
flip a plot upside down if the increment is selected to be negative

BUT whenever I try this I don't get the polygons plotted. The axes are
fine but the plotting region is wrong. Ferret seems to be mightily
confused...

I've managed a partial work arond but it doesn't appear to work for our
non ideal case.

Any ideas...

Modifying the example in the documentation

yes? LET XTRIANGLE = YSEQUENCE({-1,0,1})
yes? LET YTRIANGLE = YSEQUENCE({-1,1,-1})
yes? LET XPTS = 180+30*RANDU(I[i=1:10])
yes? LET YPTS = 30*RANDU(1+I[i=1:10])

!this works fine
yes? POLYGON XTRIANGLE+XPTS, YTRIANGLE+YPTS, I[I=1:10]  

! no polygons
yes? POLYGON/vlimits=2:30:-2 XTRIANGLE+XPTS, YTRIANGLE+YPTS, I[I=1:10]

! This is a work around for the example but I can't get it to work for my 
! real case

! Multiply the y values by -1

yes? POLYGON/vlimits=2:30:-2 XTRIANGLE+XPTS, (-1)*(YTRIANGLE+YPTS),
I[I=1:10]


Cheers,
Russ Fiedler