Funny, I've been asking myself the same question about my 50mm f/1.5 on an R-D1s - new (to me) camera, brand new lens, very hard to be sure.
But, I'm reserving judgement on mine, and on this particular image, because I can't be totally sure that I or my subjects (or you & yours, not having been there) didn't move ever so slightly and miss the focus that way. 1.5 is pretty slim DOF, of course - esp. to get two people together sharp on the same plane, I see it all the time with my Canon gear & the 85 1.2. If either you or they shifted a little, even just rebalancing your weight on your feet, that could be enough for what you're seeing in that image.
I think the only way to eliminate the rangefinder alignment question is to check other lenses on your body, and / or that lens on another body, and see if your RF is consistently out with all of them; or if that lens is consistently out with many cameras. Which can be tricky, if there aren't other R-D1s around...
Try shooting some non-moving subjects with the camera on a tripod, and see if you can pin down the problem that way; at least that will tell you if the lens / body combo is wrong, or if it was actually some movement on the night in that particular case.
Hope that helps?