Ah. That is expected behavior.
Remember, NoScript blocks everything by default. 'Mark as Untrusted' is mostly cosmetic (hiding unwanted sites from the main menu), unless you are using 'Scripts Globally Allowed'. Which is not recommended.
If you have temporarily allowed a site, then it no longer qualifies as 'I don't trust this site and never will', so it gets moved back to the main menu. It still isn't 'trusted' after you revoke the temporary permissions, it's just not hidden any more.
If you use Gmail, then you probably should not mark google.com as Untrusted. Just temporarily allow it when you need it.
And if you are indeed using Scripts Globally Allowed, then you're going to find that your options are more limited, and there are probably much better candidates for blacklisting than google.com (google-analytics.com, for starters).
Remember, NoScript blocks everything by default. 'Mark as Untrusted' is mostly cosmetic (hiding unwanted sites from the main menu), unless you are using 'Scripts Globally Allowed'. Which is not recommended.
If you have temporarily allowed a site, then it no longer qualifies as 'I don't trust this site and never will', so it gets moved back to the main menu. It still isn't 'trusted' after you revoke the temporary permissions, it's just not hidden any more.
If you use Gmail, then you probably should not mark google.com as Untrusted. Just temporarily allow it when you need it.
And if you are indeed using Scripts Globally Allowed, then you're going to find that your options are more limited, and there are probably much better candidates for blacklisting than google.com (google-analytics.com, for starters).