REGRESSION: Changing assignees in transition screen is taking into account the permission property of the CURRENT status, not the DESTINATION status

Say you have two statuses, OPEN and START PROGRESS.
OPEN has the jira.permission.assignable.projectrole property set to role_A.
START PROGRESS has the jira.permission.assignable.projectrole property set to role_B.

Transitioning from open to start progress, there is a transition screen with the Assignee field. If you try to assign to someone who is in role_B, the assign will fail with error "cannot be assigned issues". (despite the auto-complete manages to show the user as an assignable user!)

This is not the intended behavior because in JIRA 6.3.4 or older, you can assign to a user in role_B without problems, since users in role_B matches the workflow property configured in the START PROGRESS status, which is the destination of the transition.