I found a bug in the AF theme. There is a symbol for unknown gender. Turns out it looks like this: . But it's name is "?.png". Naturally, if you create an URI string like "http://foo.bar/?.png", it will parse as "/", with argument string ".png". If you change the link to the equivalent of http://foo.bar/%3F.png, or rename the image, it it will show up again.