If you post in forum that goes to mailing list, with content enclosed in square brackets, the forum will show the square brackets, but the mailing list will not. Content is completely lost on e-mail copy.
This happened to me with:
location = /base { [stuff] }
location ^~ /base { [different stuff] }
Shows up on mail like this:
location = /base { }
location ^~ /base { }
Maybe overzealous bbcode stripping bug?