This isn't quite a major bug, but its still a bug...
Everytime I try click the "Set as Favorite Category" link for any series with a four digit ID (ex. D Gray-man #1004), an error page comes up. The answer is simply that there is a comma in the number. I'm not sure if its a coding error or what, but manually removing the comma allows the link to work.
I'm not sure if this is just me alone or not, but its something I run into every so often. Just wanted to let the mods know.