I've found another bug in the Shopify POS App.
When adding an item to the cart via the cart.addLineItem method it does not respect the fact that the item may already have taxes included. Please see the following example screenshots of adding an item directly through the Shopify App and then applying a discount, which works as expected.
You can see above, the tax $4.74 is included in the item price of 52.16. This is the correct price and tax.
However, after adding the item through the Shopify POS API and then going to checkout gives me a popup saying "Updated Taxes, Taxes have been updated based on tax rules applicable to your location. Let your customer know the new total.". In this case it then adds an extra $4.74 to the total price rather than this amount just being part of the total as above. I am sure this only started happening as of 4.4 (when at least one other bug was introduced), as we use this function in our shop every day.
We are getting the same issue via our POS. It's changing the taxes (which are correct) and doing crazy things. 1. it added 25% tax to an order for no reason. 2. It reduced the tax on an order for no reason.
Better yet, it doesn't tell us why it's doing it. So we have no access to correct the problem, or avoid it.