Problem with Fields getting wrong InternalName when attached to a list through a contenttype

I found an issue where some fields when attached to a list through a contenttype gets the internalname from another fields with the same displayname. This affects the possibility to properly get changes done on the parent contenttype propagate to its child contenttypes on the lists like the order of the fields (SPFieldLinkCollection.Reorder() uses internalName).

As an example: 

1. Create a Task list

2. Use SharePoint Manager to look at the properties of the original task manager. Find the field "Due date" and take a note of the Id and InternalName (In my test these would be Id: cd21b4c2-6841-4f9e-a23a-738a65f99889 and InternalName: TaskDueDate)

3. Locate the Task contenttype in the tasklist through SharePoint Manager, Find the field "Due date" again and take a note of the Id and InternalName (In my test these would be Id: cd21b4c2-6841-4f9e-a23a-738a65f99889 and InternalName : DueDate)

If we check the available fields in the SPWeb there is secondary field named "Due Date" with the internal name of DueDate and ID: c1e86ea6-7603-493c-ab5d-db4bbfe8f96a

The conclusion would be that sharepoint can mix fields together when a contenttype is added to a list, as far as I can see this should be considered a bug in SharePoint.