Thanks, but you missed the part where everything has been working for at least a year and then suddenly it wasn't. Of course my 403 and 404 and other error pages are separate. And 404's are working but 403's not, yet the file permissions are the same.
Now that I think about it, by the very nature of an error 403 it's possible that those can't be rendered when there is an error. I'll look into that. It's like a Server Error 500. If the server was functional to give you a custom page it would probably be functional enough to avoid throwing that particular error. (No, I don't have a 500.html).
As to why not just copy all the icons? The short answer for the long-term is that I'm using a supported feature., and even for this small set of files, copying them is just a waste of disk and just more files for us to backup and lug around.
For a longer answer, I wish we had more opportunities to link to files so that we didn't all need to clone the exact same data which winds up in cache on both clients and servers. It's a major waste of resources. If just making a copy of files where a good solution, why not just create a new instance of Apache for every domain? Why not put a completely unique /etc and /var under every /home? Of course that's ridiculous - so why should I have the exact same Wordpress vX.Y, the exact same Drupal 6.2, and the exact same Gallery2 that a hundred other sites on my server have? No, copying files when it's not necessary is cumbersome - and very "un-green".
As for just copying the files now - if I just work around this issue, there might be a lot of other DH users who could trip on something similar - and maybe none, who knows? Sure, I can fix "my" problem, but 1) I shouldn't have to, and 2) that could only defer other problems that I and others won't want to fix later.
I'll give this a few days here but without any solutions I'll put in a support ticket.