In category view all manufacturers are visible, even though they are not associated with products in the category. Only manufacturers that are associated with one or more products in the category should be visible in the category view.
You're right, but actually it's not a bug, because it was designed in that way. Manufacturers section is just a manufacturer section, it displays all manufacturers. But we will consider to add it as a filter, so you will be able to see only manufacturers assigned in partucular category. Thanks for suggestion.