[Resolved] Admin Order currency unit price is wrong

Background of the issue:
I am trying to create an order via admin with currency USD on a staging site. The shop currency is THB. I added the product 17660 one pair for a customer and created the order. URL: hidden link

I had previously talked about this with Norman on post 15701722. He asked me to recreate the issue on the below environment, which I did, see order #78. However whereas in my website alt least the correct line total shows correct amount in THB, in the sandbox all amounts are shown in THB (despite the order being in USD). I created another order, #80, in EUR, and the problems are identical as in my site.
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The steps to reproduce the bug are:
1. Go to WC admin, then to Orders then create a new order
2. Select order Currency USD (or another one which is not base currency THB)
3. Add sku 17660 (I only uploaded one product to the sandbox)
4. You will see either:
a. both the line cost, total, as well as the subtotal and order total in base currency amount (not converted) (as in order #78) or
b. the line cost, subtotal in base currency amount (not converted) and line total and order total in correct amount for the currency (converted). In this a case a discount is automatically added for the difference line cost - line total. (as in order #80)

Symptoms:
The cost (unit price) is showing as $263.07 instead of $7.92, with a $255.15 discount being incorrectly applied. The unit price is not converting to USD and is using the base currency price of 263.07 THB as if it was USD. The discount appears to be the difference between 263.07 and 7.92.

Questions:
Why is the unit price, subtotal, total not converting to the selected currency (USD)?
Why is a $255.15 discount being incorrectly applied?