Section 3 say:
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Once the last element in a sequence has been returned, or the enumeration context has expired, the enumeration context is considered invalid and the result of subsequent operations referencing that context is undefined. 
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This isn't true.  Later on in the spec its very clear that a
wsen:InvalidEnumerationContext fault MUST be generated - see the Pull
section.

Proposal:
replace the above text with:
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Once the last element in a sequence has been returned, or the enumeration context has expired, the enumeration context is considered invalid and the result of subsequent operations referencing that context MUST generate a
wsen:InvalidEnumerationContext fault.
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Also, for consistency, add the following text (taken from the Renew section) 
to the Release section - under the EnumContext description:
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If the enumeration context is not valid, either because it has been replaced in the response to another Pull request, or because it has completed (EndOfSequence has been returned in a Pull response), or because it has been Released, or because it has expired, or because the data source has had to invalidate the context, then the data source SHOULD fail the request, and if so, MUST generate a wsen:InvalidEnumerationContext fault. 
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