Does the following choice violate UPA?

   <group name="grp">
     <sequence>
       <element name="e"/>
     </sequence>
   </group>
 
   <choice>
     <group ref="grp"/>
     <group ref="grp" maxOccurs="3"/>
   </choice>
"Schema Component Constraint: Unique Particle Attribution" states:

A content model must be formed such that during validation of an element 
information item sequence, the particle contained directly, indirectly or 
implicitly therein with which to attempt to validate each item in the sequence 
in turn can be uniquely determined without examining the content or attributes 
of that item, and without any information about the items in the remainder of 
the sequence. 
In the constraint above, what does "particle ... can be uniquely determined" 
mean? 

See:
http://lists.w3.org/Archives/Public/www-xml-schema-comments/2001OctDec/0072.html