Colorbar mapping colors incorrectly on complex subplot image

I have code that says:

figure;
color hsv;
subplot(511);
hold all;
heatmaptext(data1, 'COLORBAR',false); %data is a 2D matrix

%and so on for the next 4 subplots... 
%then

axes('Position', [0.05 0.05 0.9 0.9], 'Visible', 'off');
c = colorbar;
caxis([myMin, myMax]); %just the max and min of all the data used

where heatmaptext.m is the "pick of the week" submission on the file exchange.

http://www.mathworks.com/matlabcentral/fileexchange/15877-heat-maps-with-text

Its a great image HOWEVER, when I look closely I see that the colors in the cells do not align to the colors shown on the color bar (at all). eg for a colorbar with range -1 -> +1, bright red according to the colorbar is +1, whereas my red cells might have values of 0.5 (i.e. the cells should be green).

Hence something has gone wrong with the mapping.

I am pretty sure the issue is not with the heatmaptext.m code but with my attempt to put one universal colorbar on a subplot image.

Any ideas? thanks