Do you know why a color bar would display two tick multipliers? It wouldn't be a big deal if the duplicate multiplier had been positioned well, but the multiplier text is placed at a somewhat arbitrary location on the figure.
This is how I create and position the common color bar in a multi-plot figure:
set(cbhe,'Location','NorthOutside','Position',[.13 0.94 .43 .01],'FontSize', 10);
The color bar value are from 1E9 to 6E9. The color bar ticks are from 1 to 6 with the text "x 10^9" displayed on the lower right side of the (horizontal) color bar. But the same multiplier text is duplicated somewhere above the color bar to its far left as well. This seems to be happening with horizontal color bars. The vertical ones have a single multiplier.