Why are pie charts in multiple subplots black?

I have a program that generates many pie charts, each within its own subplot. Oddly, after I apply a legend or resize the figure manually, the pies all turn black so that you can no longer see the color wedges. If you follow the example below then maximize the figure so you can see the pies, they should be black. This used to work in 2010 and now in R2012a it does not. What could be the cause?

figure ; 
nCol = 23 ; nRow = 15 ; 
iPlot = 0 ; 
for iRow = 1:nRow
    for iCol = 1:nCol
        iPlot = iPlot + 1 ; 
        subplot(nRow, nCol, iPlot) ;
        pie(rand(1, 6))
    end
end
% When we reach this point and resize, pies are in color
% Some time after this point, pies switch to black
delete(findobj('type', 'text'))
labels = {'A', 'B', 'C', 'D', 'E', 'F'} ;
legend(labels) ;

[Oleg Komarov]

With no snippet of code that reproduces the anomaly I think hardly anybody will answer.

[K E]

Excellent suggestion, will update the question.

[Oleg Komarov]

I cannot reproduce the problem (but I am using the pre-release 2012b). Still, it took several minutes to complete (no dedicated graphics card).

Answer 1

[Sean de Wolski]

They're in color for me after the text deletion step (the text was in black).

[Sean de Wolski]

yeah, using: nRow = 20,nCol = 20;

[Sean de Wolski]

What renderer are you using?

get(gcf,'renderer')

[K E]

OpenGL. But when I switched to zbuffer or painters, the black pies returned to color! Time for me to learn more about renderers. I also found the figure slow to generate in opengl, and this answer has some useful information on that problem.