XML Schema: Chameleon Redefine Pervasiveness Puzzle

[Paul Hermans <paul.hermans@amplexor.com>]

Start Situation
----------------
Schema A: no target namespace
1 simpleType "T" being a union of a specific "enumeration of QNames"  
and "QNames".
Rationale: The enumeration must be restrictable and/or extensible.

Schema B: targetnamespace 'B'
includes Schema A as a chameleon
hence simpleType "T" becomes part of the namespace 'B': {B}:T
one element {B}:a has datatype simpleType {B}:T

Schema C: targetnamespace 'C'
includes Schema A as a chameleon
hence simpleType "T" becomes part of the namespace 'C': {C}:T
one element {C}:x has datatype simpleType {C}:T

Schema D: targetnamespace 'D'
imports Schema B and Schema C.

Redefine with 2 schemafiles added
---------------------------------
Schema BB: targetnamespace 'B'
redefines Schema B
by extending the enumeration in simpleType {B}:T

Schema CC: targetnamespace 'C'
redefines Schema C
by restricting the enumeration in simpleType {C}:T

Schema D: targetnamespace 'D'
imports now schema 'BB' and schema 'CC'

Functionality sought-after:
element {B}:a can use a value of the extended enumeration
element {C}:x can only use values from the restricted enumeration

Pervasive impact
----------------
Redefinitions replace the original definitions.

My question is how far this impact goes.
Possibility 1: Does the redefinition stop at the level of {B}:T and  
{C}:T in the two schemas with the targetnamespaces?
Possibility 2: Or goes it one step further by replacing the chameleon  
datatype 'T', which leads to a conflict since one redefinition is a  
restriction and the other is an extension.
Is there one of the redefenitions that takes priority than?
Anyhow, if possibility 2 is the case than I cannot achieve with  
redefine the functionality sought-after (see above).

Is there another option to implement this feature:
starting with one template enumeration (union) which can be extended  
in one namespace and restricted in a second without the use of xsi:type?

Thanks,

Paul