XML Schema multiple import effect - xsd

Question

While looking at XML schema examples, I have seen the following case (in xml schema test suite, microsoft schema schG1_a/b/c.xsd):
Conceptually, schema document A (target a) imports schema document B (target b) which in turn imports schema document C (target c).
My reading of the schema specs is that A must directly import C in order to refer to anything in C (import is not transitive). It does not. This is not an issue because A itself does not refer to anything in C or even in B. It defines just an element 'root' that is a sequence of 'any' from '##any' namespace with processContents 'strict'.
Now the problem is that the instance document schG1.xml is referring to the schema A only although it uses global elements defined in A, B and C as children of the 'root' element in A. Because processContents is 'strict' the schema A should be used to validate the instance elements (as children of 'root'). I understand that it can do it for the elements defined in A and B (directly imported in A) but I fail to understand how it can validate elements from C since they were never directly seen in A.
However the test is supposed to be valid. I am sure I must be missing something...
schG1_a.xsd:
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"
targetNamespace="ns-a" xmlns="ns-a">
<xsd:import namespace="ns-b" schemaLocation="schG1_b.xsd"/>
<xsd:element name="e1" type="xsd:int"/>
<xsd:element name="root">
<xsd:complexType>
<xsd:choice maxOccurs="unbounded">
<xsd:any namespace="##any" processContents="strict"/>
</xsd:choice>
</xsd:complexType>
</xsd:element>
</xsd:schema>
schG1_b.xsd
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"
targetNamespace="ns-b" xmlns="ns-b">
<xsd:import namespace="ns-c" schemaLocation="schG1_c.xsd" />
<xsd:element name="e1" type="xsd:boolean" />
</xsd:schema>
schG1_c.xsd:
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"
targetNamespace="ns-c" xmlns="ns-c">
<xsd:element name="e1" type="xsd:string" />
</xsd:schema>
schG1.xml:
<a:root xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="ns-a schG1_a.xsd"
xmlns:a="ns-a" xmlns:b="ns-b" xmlns:c="ns-c">
<a:e1>123</a:e1>
<b:e1>true</b:e1>
<c:e1>foo</c:e1>
</a:root>