sp.dictionary.threshold parm of spell checker seems unresponsive

[Ronald K. Braun]

I'm playing around with the spell checker on 1.3 nightly build and
don't see any effect on changes to the "sp.dictionary.threshold" in
terms of dictionary size.  A value of 0.0 seems to create a dictionary
of the same size and content as a value of 0.9.  (I'd expect a very
small dictionary in the latter case.)  I think sp.dictionary.threshold
is a float parameter, but maybe I'm misunderstanding?

And just to be sure, I assume I can alter this parameter prior to
issue the "rebuild" command to build the dictionary -- I don't need to
reindex termSourceField between changes?

My solrconfig.xml has this definition for the handler:

<requestHandler name="spellchecker"
class="solr.SpellCheckerRequestHandler" startup="lazy">
    <lst name="defaults">
        <int name="sp.query.suggestionCount">30</int>
        <float name="sp.query.accuracy">0.5</float>
    </lst>
    <str name="sp.dictionary.indexDir">spell</str>
    <str name="termSourceField">dictionary</str>
    <float name="sp.dictionary.threshold">0.9</float>
</requestHandler>

And schema.xml in case that is somehow relevant:

<fieldType name="spell" class="solr.TextField" positionIncrementGap="100">
    <analyzer type="index">
        <tokenizer class="solr.StandardTokenizerFactory"/>
        <filter class="solr.StandardFilterFactory"/>
        <filter class="solr.RemoveDuplicatesTokenFilterFactory"/>
    </analyzer>
    <analyzer type="query">
        <tokenizer class="solr.StandardTokenizerFactory"/>
        <filter class="solr.StandardFilterFactory"/>
        <filter class="solr.RemoveDuplicatesTokenFilterFactory"/>
    </analyzer>
</fieldType>

<field name="dictionary" type="spell" indexed="true" stored="false"
    multiValued="true" omitNorms="true" />

Any advice?  I'd definitely like to tighten up the dictionary but it
appears to always include terms regardless of their frequency in the
source content.

Thanks,

Ron