Usually a release would be marked for a stable release after a decent amount of testing... so, it should be relatively bug free. Having a new release just a few hours after this one doesn't instill a lot of confidence in their testing.
From the mailing list this is an npm fix mostly for OSX:
The main fix here is letting users on Mac to upgrade globally installed modules. Also the linux binaries have been rebuilt with an older glibc so people with older systems will actually be able to use it.
To me it also means "stable API", which means published APIs are neither removed nor their function signatures changed (cough Ruby).