I find that my 1960s dual-scale Elmar 50/2.8 in M-mount collapses safely on the R-D1.
But I've been told that that's the only one that does -- the various M and LTM 50/3.5 versions as well as the modern Elmar-M 50/2.8 all risk encountering the cam roller, light baffles, etc. on the R-D1 and other non-Leica M cameras.
::Ari