Deleting a scheme with associated projects in global permission settings gives an error

In global permission scheme settings:

1. Find a scheme which has a project associated with it.
2. Click the delete link on the scheme, a page is shown which explains that the project will be reassociated to the default scheme
3. Confirm the deletion

Expected: the scheme is deleted and the project is reassociated
Actual: an error is shown saying the scheme cannot be deleted when it has an associated project