Hi Laura,
I’ve just re-checked it on my test server, but unfortunately couldn’t reproduce the issue. After adding 1.5 to the cart, the quantity in PayPal also shows 1.5, so it seems to be working fine here. I even tried to complete all the order to the end and it still shows 1.5 in my PayPal payment receipt. I’m using standard PayPal gateway (in sandbox mode) that comes with WooCommerce. Maybe you could send me the screenshot of the issue? Also – if possible maybe I could login to your server’s admin to check what’s going on? My private email is [email protected]