Subtotal price for product incorrect

We are using a custom t-shirt designer for our website. If we add the same item twice, the price of all the products with the same name (but a different design) will be changed to the last made t-shirts price. The subtotal the customer needs to pay is still correct but the price of the product is shown incorrectly. This didn’t happen on our old site with a different theme. I’ll attach some screenshots so you can see what’s happening. In the first screenshot you see me add the first t-shirt (with the small text) and it should be priced 10.49 and the 2nd t-shirt should be priced 20.49 but the first shirts price is also changed to 20.49 while the total price is still correct (i put a circle around the total price you need to look at).