Why is the USPS priority label showing incorrect weight for my package?

[Turlockyarnshop]

I’m having an issue with shipping with shopify; this is a 2.6 lb box.  The weight is correct on the ‘shipping weight’ line, but when I go to purchase the label, it looks like it’s for a weightless (0.0 lb) package.  Of course, my post office isn’t accepting it like this, so I had to void the label.  I can always ship it from the post office and pay retail, but I will have to eat the difference in cost.  The customer received free shipping on this order.

Any suggestions?  So far I’ve tried entering the weight as ounces, as grams, using the website, using the iPad app.  It seems to be doing this for both UPS and USPS; for UPS it’s showing a base price of $8.48 and USPS Priority it shows $8.52; for an order this weight I was expecting around $25 even with the shopify discount.

[SwatiSwoboda]

Can you help me understand the problem - the weights seem to be aligned? I don't fully understand how the expected behaviour is different than from what you are seeing.