Protocol: present filter behavior

In Protocol Section 4.5.1.7.5 (SearchRequest.filter.present) it says
that a present match evaluates to "FALSE ... including a presence test
with an unrecognized attribute description".
 
It doesn't mention the case where the attribute description is
recognized, but the present match is not implemented for it.
 
Section 4.5.1.7 indicates that this would result in an "Undefined"
filter item, but I'm not sure if this is the intent for present
matches.
 
So, two questions: 1) Is this case treated as Undefined? (My read says
yes). 2) Does this need to be clarified in the I-D?
 
Jim