The r/r2 and i/i2 filters are coadded toghether in the processing.  These filters are similar but not identical and introduces a photometric error of about 1%.  It can be larger for very red objects or objects with exotic colors.  The plots below shows the fraction of r2 or i2 for each patch; fraction=1 means that a patch has only r2 or i2 filter data,while fraction=0 means a patch has only r or i filter.