Like i said before i have an original 50mm non-c lens... and it does have the floating element. matt never said his doesn't have a floating element....
the only non floating element 50mm lens is the
50mm 4.5 w for the RZ67
ALL 50mm lenses for the RB67 have had floating elements...
when people complained about corner sharpness at close ranges with the 50mm 4.5w.. mamiya introduced the
50mm 4.5 (with ULD) Ultra Low Dispersion glass... it's just a lens coating (nothing to do with the re-introduction of the floating element)
as for not being sharp with a 50mm on an RB, that sounds like being unaware of the floating element, or bad/abused/heavily used copy as mentioned above