Thanks BobYIL. Marek focussed at one meter in his tests. His 1.5 optimized lens started back focussed slightly and moved further back. Mine has maximum focus in front of the rangefinder focus point at 0.9m and moves backward as i stop down. As you say, the range is the same, but the usefulness of straddling the rangefinder focus point is probably why I have had no problems with the lens in practical use.
My previous experiments were too inexact to draw any conclusions from but this one is useful to me. I guess anyone owning this lens who has noticed problems might benefit from a similar examination. If there are no problems in practical use I wouldn't recommend looking into it.