MacOS – Permissions of /Users keep changing back to drwxrwxrwx

Many factors might come into mind. A process with root privileges is the main cause.

Think about an Application that you grant permissions to install using your Admin password. This Application might not have permissions set properly for certain folders that are installed in key OS location (i.e. /Library) would cause the permissions to change.

Think about a process in an Application that is granted a root privilege and does tamper with permissions in folders incorrectly.

The idea of locking the permissions is nice, but that would be implemented at this time with a no-write permission. Unless of course there is lock-permission-only flag is used; something I don't know if it exists.

It's possible that this is a message that you can safely ignore.

There is an Apple KB article for OSX versions 10.6 and below that itemises those error messages that can be ignored, however that message is not in the list. I cannot find an updated KB article for 10.7.

If the message does concern you, I'd suggest you reboot and hold down the Option key, you can then enter into Lion's Recovery mode from the menu shown and see if that does the trick.