Interesting. Fixing this would require a significant change to the way xmax and xmin are implemented. I would need to make new histograms with fewer bins and copy the content over. Currently, I just use SetRangeUser to change the viewing area.
It may be worth changing this, but it probably won't happen quickly. I'm planning to move rootplot over to the rootpy project (https://github.com/ndawe/rootpy), which takes the approach of wrapping root objects with some python niceties. I will be doing a substantial rewrite of rootplot when I port it over, so I think this issue will wait until then.