[Gnuplot-info] effect with label

[Pedro C. <ped...@gm...>]

Dear Gnuplot Users

I have some strange behavior (or maybe not) using a label on a pm3d map
projection. Example:

set term post enhanced color
set output "spectrum3d.ps"
unset border
f(x)=x-1
set palette color
set pm3d map
set xrange [1:13]
unset ztics
unset ytics
unset xtics
set samples 201
set isosamples 2
set size 0.8,0.2
unset key
unset colorbox
set label 2 "M" font "Helvetica-Bold,12" at 2.15,graph 0.5,graph 1 center
front tc rgb "black"
set palette model RGB defined (1 "green", 1.25 "dark-green", 1.25 "yellow",
1.33 "dark-yellow", 1.33 "red", 4 "dark-red" )
set origin 0.0,0.5
splot f(x)

If I run gnuplot (version 5.1 and 5.2) on the right side of the plot appear
an extra line (see pdf "plot_withlabel.pdf" created from the postscript
file). If I comment

set label 2 "M" font "Helvetica-Bold,12" at 2.15,graph 0.5,graph 1 center
front tc rgb "black"

no such feature appears (file "plot_withnolable.pdf".

Is it something associated to the boxed label option or some bug?

Pedro