Well, it sounds like your mail carriers have large sticks in their rectums. And for that i pity you.
A few points:
Whether or not it is actually a requirement of law that you stay away from locked mailboxes while the mail carrier fills them, these sorts of group mail delivery areas are major vectors for theft and there is no way for a postal carrier to know whether or not you are actually the legal recipient.
Thus, the logical cover-your-arse regulation is that everyone should just keep out until the postal carrier cannot in any way be seen as having helped anyone posess anything. You see, if they turn their back and walk away, it's none of their business if you happen to have a stolen key and steal someone's mail. But if they stand there and watch you do it, someone could argue that they should have stopped you. It's even worse if they just hand it to you. Even if they do actually know you.
As of this point in this post, I'm done sticking up for the post office. I do in fact have an axe to grind with them. I've fought the post office and won, and I'm here to tell you that they're full of crap.
The USPS exists in a bizarre legal limbo between private enterprise and federal entity. The truth of the matter is that the postal carrier's rule book - The Domestic Mail Manual - is in fact the law of the land.
There is a federal law that states that the DMM is regarded as law, and revisions to the DMM are reviewed and included only if approved by congress.
This is where we get legal paradoxes like the fact that you own your mailbox, but the post office regulates it and has the force of law to do so.
The rub is: The DMM does not say everything that the USPS wishes it said.
In my case, when i bought my house almost two years ago, I decided that having a rural-style (long tube) mail box bolted to the side of my house where the fence meets the siding next to the front porch is both tacky and stupid, and bought a mailbox more appropriate for the architecture of the house - i bolted it to the siding about 20 inches from where the original mailbox had been.
I received several warnings from the post office that this change was illegal.
And then they stopped delivering my mail. Instead they would leave little cards in it instructing me that i live on a rural route and thus am required to have a rural style mailbox on a post at the edge of my property line.
After several fruitless arguments with the supervisor for my zip code, with the supervisor arguing that i cannot move my mailbox, I downloaded a PDF of the DMM and could find no provision in it that required me to have a rural mailbox.
I do in fact live in a historic district. I live in one of the oldest houses in this city. The DMM states, for example, that mail-slot delivery is only legal where it has existed since the by-gone age when mail slots were normal. A quick wander around my neighborhood revealed that about 30% of my neighbors have only the original mail slot for mail delivery.
It does state, explicitly, that the post office has the right to demand any legal method of delivery for new construction. This is why most new developments have group kiosks.
So i called the supervisor again and asked him to explain which provision in the domestic mail manual allowed him to require that i use a rural mailbox.
He told me that any "new residence" can be required to change, and they are interpreting that as meaning that any time someone moves in, the post office can require a change in delivery method.
I informed him that i was reading the DMM and it says new construction, not new residences. And that if my mail delivery was not resumed, I would register a formal complaint with the district manager.
After an uncomfortable pause, the supervisor completely changed tracks and stated that the issue was that i had moved my mailbox from the fence to the house.
I countered that i could prove that the mailbox has never been attached to the fence (it was in fact bolted to the house mere milimeteres above the fence), and that i had only installed the new mailbox about 20 inches away.
He decided that that was ok.
My mail delivery was resumed the next day.
I sorely wanted to mail myself a slab of lead in a flat-rate mailer, just to make the carrier really *feel those steps all the way to my porch, but ultimately i decided that since i would have to mail it in person at the post office, this would be awkward.
It turns out, this isn't the worst that this particular post office has tried to pull.
A friend of mine says that his mail delivery just stopped one day. He'd lived in the same house for 8 years, and it just stopped.
When he called the post office, they explained that he needed to use the kiosk at the new development two blocks away.
His story is a lot like mine, and his solution boiled down to the same two steps:
1: Read the DMM
2: Threaten to speak to the district manager.
Last year the house south of me sold, and somehow, they conned the new owner into putting a mailbox on a post at the sidewalk. What a maroon.