Inventory problem with WooCommerce

Hi,

Im facing this strange issue, when the Inventory is enabled and the product is a variation even it is on stock and purchasable the WooCommerce think that it is Out of Stock.

Backend Inventory Management enabled:
https://snag.gy/grO0sp.jpg

For example this product, every variation is in stock, but if you choose the dropdown the availibility is Out of Stock:
http://bodybulldozer.lastminute-utazasok.hu/produkt/scitec-nutrition-zero-iso-great/

Inventory Management at Variations: Backorders are not allowed. Is purchasable, inventory is enabled and there are 3 pcs for 2300g/vanilka variation
https://snag.gy/vzPNbn.jpg

Can someone help me with this issue? Do I need to enable the inventory management at product level too? I mean this:
https://snag.gy/N0VyG7.jpg

Thanks for all the help.

Regards,
Peter.