Paypal onShippingChange / patch not working as expected - paypal

Question

I find that there is precious little Paypal help online when things are behaving badly, and I am having some trouble with onShippingChange() and actions.order.patching. When I run the following code with the new Paypal buttons, return actions.order.patch() doesn't seem to work properly.
My code is below:
<script src="https://www.paypal.com/sdk/js?commit=false&client-id={sandbox-merchant-id}&disable-funding=paylater&currency=USD"></script>
<script>
paypal.Buttons({
createOrder: function(data, actions) {
return actions.order.create({
"purchase_units": [{
"description": "Sporting Goods",
"amount": {
"currency_code": "USD",
"value": 12,
"breakdown": {
"item_total": {
"currency_code": "USD",
"value": 12
},
"shipping": {
"currency_code": "USD",
"value": 0
}
}
},
"items": [{
"name": "Arizona Christmas",
"sku": "sku01",
"quantity": "1",
"unit_amount": {
"currency_code": "USD",
"value": 12
}
}]
}]
});
},
onShippingChange: function(data, actions) {
const baseOrderAmount = '12.00';
if (data.shipping_address.state == "AZ") {
const shippingAmount = data.shipping_address.state === 'AZ' ? '50.00' : '60.00';
return actions.order.patch([{
op: 'replace',
path: '/purchase_units/#reference_id==\'default\'/amount',
value: {
currency_code: 'USD',
value: (parseFloat(baseOrderAmount) + parseFloat(shippingAmount)).toFixed(2),
breakdown: {
item_total: {
currency_code: 'USD',
value: baseOrderAmount
},
shipping: {
currency_code: 'USD',
value: shippingAmount
}
}
}
}]);
}
}
}).render('#paypal-button-container');
</script>
With the above code, when I change from a default California address to an Arizona address (in order to cause a change in shipping costs), the onShippingChange(...) event fires immediately, then the Paypal window shows the "processing" loader, then shows the new total in the upper right corner. The Paypal window itself shows $62 (as expected), but when I expand the total price breakdown, it shows $0 for shipping. Also, console.log(data) shows nothing updated... all the original dollar values. So it appears that the details of the .patch are not being applied completely.
But then there is a strange thing I notice. If I hit F5 to refresh the Paypal window, it refreshes, of course. The total cost and breakdown become correct (shows correct total, shipping, etc), and the console.log(data) shows the correct breakdown, but then the address is back to the original address (a California address; that is the default address for the sandbox personal account).
So... I'm not sure what to make of this. Am I doing something wrong with the code above? Or is Paypal's system just not quite refined enough to use the new Buttons Javascript-only based solution (vs. the server-side solution)? I can't do the server side solution, so I'm hoping to get this to work properly using the plain javascript sdk implementation.