Highlighting not working on a prefix_token field

[Avlesh Singh]

I have a "prefix_token" field defined as underneath in my schema.xml

<fieldType name="prefix_token" class="solr.TextField"
positionIncrementGap="1">
    <analyzer type="index">
        <tokenizer class="solr.WhitespaceTokenizerFactory"/>
        <filter class="solr.LowerCaseFilterFactory" />
        <filter class="solr.EdgeNGramFilterFactory" minGramSize="1"
maxGramSize="20"/>
    </analyzer>
    <analyzer type="query">
        <tokenizer class="solr.WhitespaceTokenizerFactory"/>
        <filter class="solr.LowerCaseFilterFactory" />
    </analyzer>
</fieldType>

Searches on the field work fine and as expected.
However, attempts to highlight on this field does not yield any results.
Highlighting on other fields work fine.

Any clues? I am using Solr 1.3

Cheers
Avlesh