When grouping items using a property that can have the
value of None,
batch.propchanged appears to return a false value
instead of a true one when the property value changes
from "None" to "1" or from "None" to "1".

The property I am indexing on is called category, and
what I get on the
index page is headers for "no category set", and for
the categories
with order values of "2", "3", and "4", but no header
for the category with order value "1".  If sorted in
descending order, we get the headers in the
order "4", "3", "2", "1", with "no category set" missing.