Calculation of free-shipping threshold seems incorrect when doing currency conversions

[anatomie]

I've set free shipping for. orders more than £25. This works well, if the customer is shopping in GBP. However, I've tested my site in other currencies and it doesn't work as expected. Taking AUD as an example, I can compute the expected free shipping threshold as exchange_rate * 25, which is 48.61 using the exchange rate from Shopify > Settings > Payment. I created a product of price £24.25, which is $48.00 if I use the same exchange rate and account for rounding up to the nearest dollar. This is under the free shipping threshold, however at the checkout Shopify still offer free shipping.

Is this a bug in how the cart values are converted between currencies at the shipping page? I only carea about this because I'm trying to tell my customers how much more to spend to get free shipping, but I can't do that if I don't know what the free shipping threshold is in different currencies.

Thanks!