My shop is version 1.5.0. I had an order from Texas and Paypal Express added a sales tax when there should not have been a tax. There is a sales tax showing in my paypal account for this order. I checked previous orders from this shop and no sales taxes were applied. This is something new that happened.
I have two zone definitions set up. One zone is for insurance, zone define, no tax setting (yellow icon), which is set for all zones. The second zone definition is sales tax set up for RI, zone and taxes defined (green icon). The details show that Rhode Island is the only zone selected, not all zones. To test I went through the checkout process and when I get to the paypal payment form there is a sales tax (RI 7%) being applied which shows in the order summary, even though there isn't a known zip code at this point.
Configuration > my store > basis of product tax is set to shipping.
I haven't added any new modules to my shop in quite a while to account for this problem. I don't recall having made any settings changes in admin which might cause this. I checked my shipping modules to see if tax was being applied to shipping fee and that is set to none. I set the RI tax rate priority to 1 and that doesn't make a difference. I checked my paypal account and there were no taxes set up in there so I set up a tax rate for RI to see if that would make any difference but it did not. I changed my insurance zone from all zones to just guam to see if maybe paypal is picking up the tax amount from that but tax is still being applied.
I also have a 1.3.9h shop using paypal express and this sales tax problem isn't happening. No sales tax is showing in the order summary on the paypal payment form and orders outside of RI are not being charged sales tax.