workflow post function dropdown has invalid filter when selecting user

I am setting up a new project, so first I need to set up a new workflow for it. One of the things I need to do is add a post function to the workflow to automatically assign issues (when being resolved) to a particular user. I will be doing this in conjunction with a field configuration scheme that hides the Assign-To dropdown on resolve issues screen.

Everything is fine except for one thing. In the workflow browser (which was hard to find, by the way) for Transition: Resolve Issue, I choose to Add a new post function to the unconditional result of the transition. Then I choose to "Update Issue Field ==> Updates a simple issue field to a given value." On that screen, I choose the field to be "Assign To", and the drop down for the field shows a list of users. All well and good except for one thing. It shows a list of users based on Assignees for a particular project, and it's got a project shown there that I haven't even worked with recently, and isn't even numerically first. It just seems to be a random project.

So, I'm in a catch-22. I can't save the workflow for the project I'm about to create because the user doesn't appear in the drop down. And I can't create the project with that workflow and then change it because I can't edit an active workflow. As a workaround, I added the user I needed to the assignable user list of the project JIRA decided to display, created the workflow, and assigned it, and then removed that user from that group.

But I shouldn't have had to do that. The dropdown should simply display a list of users.