I've had this issue for a few months, where upon attempting a password change I'm simply met with a "You must complete the entire form" error. Thing is, the entire form is complete. I've tried random reset, but now I'm just stuck with a long string of letters and numbers.

Is the password changing system broken, or am I missing something obvious?

Works for me. There are only three fields you need to fill out on that page, just ignore the email section.