Just thought I would answer my own post by mentioning that it isn't a bug with Cell Stats but a problem with the person who wrote the above code 😉 For those interested here is the way it should be....rasterlist = []
for rasters in arcpy.ListRasters():
rasterlist.append(rasters)
outcellstats = CellStatistics(rasterlist, "MAXIMUM", "DATA")
outcellstats.save(output + "maximum_2006")