Website 404s with special characters used in password. Is this a vulnerability?

I found a website that 404s whenever I use a '>' in the password field. Could this be a vulnerability or is it just terrible programming practice?

Error 404--Not Found

The error screen I get:

From RFC 2068 Hypertext Transfer Protocol -- HTTP/1.1:

10.4.5 404 Not Found

The server has not found anything matching the Request-URI. No indication is given of whether the condition is temporary or permanent.