Solving confusion around welcome email link only valid once

We have implemented Zendesk end user support with SSO only.  One oddity that we found is that the link in the welcome email that is sent out is good one time only. If for any reason, the customer clicks that link and then doesn't sign up, if they click it again it takes them to the "Zendesk user change your password" screen which is the wrong place. Zendesk support says it is working as expected but it is confusing to our customers. There are 2 cases we have seen this. The first is if the customer has an issue signing up the first time or doesn't finish and then tries again later. The other is that customers forget the link to our support system and try to use this link to go back to it.  In both cases, when they click it they end up on a screen that isn't relevant and suggests they can change their password which if they do, does nothing because we do not use Zendesk security.  |

We have added tips in the email and in our online guide, but that's not really effective since people don't read those details...

Looking for tips from others that might have gone down this path.