Price before discount shown even when there is no discount

[stawebnice]

Hi,
I have eshop on VM 3.0.8 at test site: http://www.nova.pippy.cz/eshop
I am dealing with this problem - we want to show the price before discount crossed only when there is some discount on category and product detail

now it is shown on some products:
http://imtp.me/9emy02lj3  which looks stupid when there is no discount

strange thing is that there are two products with identical price settings:
http://imtp.me/9en002lj3.p

but one has the original price crossed and one does not
http://imtp.me/9en102lj3

Please advise, what could affect it?

[stawebnice]

I asked the customer and she said that this product had a discount in past,but no discount is  assigned to it now, in DB it shows -1. I deleted all discounts from database except for VAT. Is it possible that there is a bug in VM 3.0.8 that it shows scratched price  even if the discount is no longer valid?