bug in display # of products dropdown

[screamintrees]

hi could you have a look at this bug ?
i have enabled the use of mambots/plugins in the VM admin then i wrote in a category description {loadposition user2} but the plugin won' display.
the funny thing is that when i change the display # to any other than default the plugin begins to work !!!
Shows up also the default modules i associated with the link "Buy here"

could you please have a look at the link below, where the bug is reproduced ?

http://liguebrasilusa.com/index.php?option=com_virtuemart&page=shop.browse&category_id=7&Itemid=&lang=us

I desperately need this to work out

thanks!