<fieldType name="commaseparated" class="solr.TextField">
    <analyzer type="index">
        <tokenizer class="solr.PatternTokenizerFactory" pattern="[^,]+"/>
    </analyzer>
    <analyzer type="query">
        <tokenizer class="solr.PatternTokenizerFactory" pattern="[^,]+"/>
    </analyzer>
</fieldType>

<field name="opts" type="commaseparated" indexed="true" stored="true" />

Case 1:  {"opts":"important_grp_mk"} - Not working
Case 2:  {"opts":"important_grp_mk,read_grp_mk"} - Working