quantity button not work on shop.browse??

[ZEUS__]

hi,
I use Joomla! 1.5.6 and Virtuemart 1.1.2.
I put some feaured products on pages and I realize that quantity button on "child category's featured products" not work.at first link there is main category "page=shop.index".at bottom of page there is some featured products and quantity button works and there is no problem.
http://localhost/tuntun15/index.php?page=shop.index&option=com_virtuemart&Itemid=2

but at the second link's page "page=shop.browse", there is again some featured products at the bottom of page but quantity button not works..
http://localhost/tuntun15/index.php?page=shop.browse&category_id=170&option=com_virtuemart&Itemid=2

is there a way to fix it?

P.S: I open this topic on general question but no answer by someone..I think this is the bug area.so I open this topic again here.please say me it's a bug or not..or may be I have some problem with my codes..in fact I couldn't changed nowhere bu I'm confision