Should Files.createDirectory allow setting of group and other permissions?

[Tim Fox]

I am calling Files.createDirectory() to create a new directory with a 
set of Posix file permissions, on Linux. Here is some example code:

String perms = "rwxrwxrwx";
String dirName = "some-dir";
FileAttribute<?> attrs = 
PosixFilePermissions.asFileAttribute(PosixFilePermissions.fromString(perms));
Files.createDirectory(Paths.get(dirName), attrs);
System.out.println(PosixFilePermissions.toString(Files.getPosixFilePermissions(Paths.get(dirName))));

Prints out "rwxr-xr-x", not "rwxrwxrwx"

If I change perms to "r-xrwxrwx" then it prints out "r-xr-xr-x"

I.e. it seems when creating dirs the group and other permissions are 
ignored, and only the specified user permissions are set.

Can anyone clarify whether this is expected behaviour?

Thanks