stockable plugin cart variant not visible when product is added to cart

[GuidoS]

When I add a product to the cart after choosing a cart variant, like size and I go back to that same product I don't have the custom variables anymore. Only the add to cart button is visible. When I delete the product from the cart and go back to the product the custom variable is back. The setting for order is that set to "Can always order a product".

Joomla 2.5.27
VM 2.6.12