Hi Mike,
The number that is getting set (~9.92e6) is just one bin off from the maximum value (you have a range of 2e7 and the default is 256 bins). The code that displays the colorbar, as best I can tell, occurs when you call save_annotated. This method eventually calls ColorTransferFunction.vert_cbar where the ticks and limits are applied to the colorbar axes object.
Looking over the logic in that code, it is not immediately obvious to me why the index is off. I suspect is has something to do with how the `visible` variable is defined, but I'd need to play with a dataset and some print statements...
Chris