This probably isn't clear, since there's no man page for
d.leg.thin, but if you use the "smooth" flag (-s or -sm for
mouse placement of legend), then the thin and lines options
are ignored. Only when drawing a discrete legend with boxes
and categories are these two options used to thin out (thin=)
or truncate (lines=) the number of legend boxes.
If you are not using -s and thin or lines still doesn't work,
it's probably a bug - tell me what machine you're using and
send me a copy of the color & range files for the map.
- Bill