After the launch of an SLBM from the Ryazan submarine on August 1, 2008 the Navy for some reason did not announce the type of the missile. Even though it was unlikely that the missile was anything but R-29R, the reason for this secrecy was unclear. Now the Makeyev Design Bureau confirmed that it was an RSM-50/R-29R missile. However, as it was suspected, it was a somewhat unusual missile - according to the report, it carried a "modified instrumentation section". It's not quite clear at this point what that means but I hope we'll find out.
UPDATE 08/05/08: I checked the post on the previous R-29RM launch - at the time the Navy said that the test had something to do with "reliability of the command and control system". Which makes me wonder if this is what the "modified instrumentation section" was all about.