lexemes in prefix search going through dictionary modifications

I am currently using the prefix search feature in text search. I find
that the prefix characters are treated the same as a normal lexeme and
passed through stemming and stopword dictionaries. This seems like a bug
to me. 

db=# select to_tsquery('english', 's:*');
NOTICE:  text-search query contains only stop words or doesn't contain
lexemes, ignoredto_tsquery 
------------
(1 row)

db=# select to_tsquery('simple', 's:*');to_tsquery 
------------'s':*
(1 row)


I also think that this is a mistake. It should only be highlighting "s".
db=# select ts_headline('sushant', to_tsquery('simple', 's:*')); ts_headline   
----------------<b>sushant</b>


Thanks,
Sushant.