Hi Surajit I aint sure if this is any help, but I had a similar problem but with stop words, they were not working with dismax queries. Well to cut a long story it seems that all the querying fields need to be configured with stopwords.
Maybe this has the similar affect with Synonyms confguration, thus your copyField should be defined as a type that is configured with the SynonymFilterFactory, just like "person_name". You can find some guidance here: http://bibwild.wordpress.com/2010/04/14/solr-stop-wordsdismax-gotcha/ Gary
