I was just able to use the link I was emailed last week to change my password a second time. Once I followed the link, it told me the link would expire on a date in the past, and then let me go ahead and register/change password just like it did the first time I used it.
I tried to reproduce this behavior but when I click on the link after registering, I get this message:
You have tried to use a one-time login link that has either been used or is no longer valid. Please request a new one using the form below.
It looks like this is working as it is supposed to.