It has been suggested that because of the slightly different standard for nominal 50mm lenses of the Leica and Contax/Kiev systems, Leica-mount lenses from the former Soviet Union (FSU) might be incompatible with Leica-brand cameras. See Dante Stella's site for a discussion.
I've found that my Jupiter-8 (many) and Jupiter-3 50mm, Jupiter-12 35mm, and Jupiter-11 135mm and Jupiter 9 85mm lenses couple perfectly to the Leica rangefinder (as shown on groundglass on a Leica M3 camera with screw/bayonet adaptor) throughout the range of focus. (Assuming the lens is correctly shimmed for backfocus. Most likely true with wideangle and normal; should be checked with teles, because it is so easy to unscrew the optical blocks, switch mounts without reshimming, lose shims etc.)
I suspect that most complaints about Russian optics can be traced to incorrect back focus...incorrect shimming between optical unit and focusing mount. (Assuming the camera lensmount is within specification, and sometimes it isn't.)