Gift cards counting towards free shipping

I’m using the Flexible Shipping plug-in to determine the rates for shipping and standard WC flat rate for local delivery (including free delivery).

I noticed a gift card in the cart counts towards free shipping. At first I assumed this problem was (only) related to the Flexible Shipping plug-in. The problem is described here.

I just discovered the problem also appears when using the standard Woocommerce flat rates. I deactivated the FS plug-in to be sure and the problem still exists.

A summary of the problem:

1. If I only add a gift card to the cart, no shipment options are available and no shipping fees are added. Just as expected.
2. If I add other items to the cart as well, the value of all items is taken into account for the free shipping threshold. My free ‘shipping’ threshold is set at EUR 50. If I add physical products amounting to EUR 25 to the cart, shipping fees will be EUR 2.95. Adding a gift card with a value of EUR 25 on top of that, will result in free shipping. This is not what I expect as a gift card has nothing to do with shipping.

Customers could take advantage of this situation:

Suppose they add physical products to their cart amounting to EUR 25 and a gift card amounting to EUR 25. Then they are entitled to free delivery. Their next order could have the same contents and be partially paid with the first gift card. In this case I have only sold products amounting to EUR 50 and can expect EUR 25 for future orders. Overall the threshold has only been reached once, but I have to deliver both orders for free. Imagine what happens if someone keeps repeating this process.

So, how do I prevent the value of the gift card counting towards free shipping?

Note: I do know I can prevent gift cards being paid with gift cards. That would actually prevent the endless loop in my example. The problem remains though.