I'm hesitant to call this a bug and do so only because it was particularly annoying. If the powers that be want to retag as feature request, I'm fine with that.
This morning, I went to update an answer and got the "SO offline for maintenance" page. So I thought, okay, I spend too much time here anyway, I'll come back in an hour. When I came back and hit
F5 for page reload, it was still offline. Same deal two hours later.
Hmm, I thought, then I noticed the URL in the address bar was a funny one and, upon going to the "real" SO front page, it was back.
In other words, I'd just been reloading the error page. For all I know, SO had only been down for a couple of minutes.
Now that error page has a link on it to retry but it seems to me that's less intuitive than just about every other site I use where F5 will reload the page you asked for (assuming the error's been fixed), not the error page you got.
Now that I know this, I won't be using F5 again in a hurry but it may catch out others, so I'm raising an issue.