Jordi Boggiano had the "pleasure" of discovering a small quirk with PHP's glob function in an application he was working on - watch out for directories that contain square braces, they won't return in the results!
Working on some personal project that lists a bunch of stuff on my hard drive, I found out that directories that contain square brackets (those ) don't return any results for the simple reason that glob reads [stuff] as a character class, just like in regular expressions. When you know it it makes perfect sense, but when you don't, the documentation is really not so helpful. Of course it mentions libc's glob() and unix shells, but not everyone knows what that implies at first glance.
He tried a few things to get around the bug (including escaping the brackets in the directories) but ended up writing a function (glob_quote) to handle the escaping of all of the meta-characters glob might need to escape to return all of the files and folders correctly.