Update workflow PostFunction does not show all users

We have workflow transitions with a simple Update PostFunction that changes the AssignTo field to auto-assign the issue to a particular user.

We just upgraded from 3.3 to 3.6 and I noticed the poplist with available users has changed. I mean the poplist that is presented when editiing the PostFunction of the workflow step.

In 3.3 it used to show all users, now in 3.6 it only shows assignable users for the projects the current user is also assignable for.

The workflow I'm editing is specific for a single project in our JIRA installation. The Jira administrator is NOT an assignable user for that project. This means that the assignable users for that project are not shown in the poplist.

I now have to make the Jira administrator an assignable user, which is not what I want to do