Problem in graphic properties management with callbacks

[goudier at free.fr]

Hi,

I have a problem to set color of polygons in a callback function :
With one polygon as above example "Mono_Spot.sce" it works perfectly.

When several handles of polygons are setted in a slider callback,
 colors sets of polygons are not well done.
See malfunction with example "Spots.sce" attached file.

Is it a bug ?

Regards
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Example : Mono_Spot.sce

function set_R ();
     set(pr,'background',color(sldr.value,0,0)); // set polygon color in
callback
endfunction

L1=sqrt(3);L2=2*L1;L3=3*L1;
X_R=[0 -2 -3 -2];Y_R=[0 L2 L1 0];Y_R=Y_R-3*L1/2; // points of polygon
lines(0);
fg=figure('backgroundcolor',[0.59  0.96 .99],'figure_name','Spots');
fg.figure_position = [700,100];
fg.axes_size = [480,280];
fg.children.data_bounds = [-18,-8;6,6];
fg.children.isoview = "on";
xfrect(-4,8,18,18);  // black screen
// Control Slider
sldr=uicontrol('Parent',fg,'style','slider','MIN',0,'Max',255,'Position',[40,60,20,140],'callback',"set_R");
xfpoly(2.5*X_R+5,2.5*Y_R,1);pr=get('hdl');pr.thickness=0; // polygon pr handle

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