Hi Joe,
When the Blog has all of the "navigation" options deselected in the settings and the "Navigation on Right" option is not enabled, the blogcenter-leftnav class is added to the blog content. If you enable the "Navigation on Right" option, the blogcenter-nonav is set which is the desired effect as all of the "navigation" options are disabled. Could you make the blog follow the same logic regardless of whether or not the "Navigation on Right" option is enabled.
I hope I explained that well enough, holler if it is confusing.
Thanks,
Joe D.