Why does my Product Personalizer output wrong image size?

[Nemanya]

I've been using the Product Peronalizer to create customizable artwork. The final product are prints.

The problem occurs when a customer makes an order. The artwork I get as the output is not the correct size - doesn't match the image size that is used as one of the layers in the product configuration.

For example, the original image is 18 x 12 in, and the output is scaled down to 3.5 x 3.5, and it has white extensions to fill up the format (because the original is 3:2 and output is 1:1).

Does anyone know what might be causing this? It is very frustrating!