[ALUG] Why does permission on home directory affect ssh?

I just spent a long time diagnosing why I couldn't get a public key ssh login to work. It eventually transpired that ssh doesn't allow one to have group write permission on one's home diectory. That's *not* the permission on the .ssh directory, it's the permission on the one above that. A quick Google search confirms that this is the case, ssh refuses to do public key authentication if the user's home directory has group write permission on it. I can't see any way to disable this (turning StrictModes off seems to disable too much) and I don't really understand the reason for it either. I only want group write set on one particular user, can anyone suggest a way to allow ssh public-key login to that user? -- Chris Green