Permissions on Process Type Actions

How is access to Process Type Actions controlled?

 

I have found that giving a user the ServiceDesk.Pages.FullChangeView permission gives them the ability to only use the "Edit Change Plan" and "Add Bulletin Board Entry" process type actions when they have an implementation task assigned to them.  The user is a member of the All Users group and I don't think it has permissions from anything else.  No direct permissions are set for this user.

 

Looking at the Change Management process type actions (PTAs), I can see these default PTAs have the "Is Edit Action" tick box set:

Edit Change Plan (*)

Manage Related Configuration Items

Manage Related Processes

Add Bulletin Board Entry (*)

Search Knowledge Base

 

But only the two with (*) next to them are available in the PTA webpart.  Why is this?  Is there a way to control which PTAs are available based on permissions?