-Byc in polar plots draws straight lines instead of arcs

[Esteban82]

In a polar plot (-JP), using custom radial ticks with -Byc causes the grid lines to be drawn as straight lines instead of circular arcs.

cat << EOF > layers.txt 
100	g
2000 g
3000 g
EOF
gmt basemap -R-45/45/0/3731 -JP6c+a  -Ba -Byclayers.txt -png lixo

rm layers.txt

I think I could try to fix this but not right now.