Shipping calculations wrong on large orders

[hedera]

I'm using zone tables, store pickup, and an attribute-controlled "free shipping" module that isn't in this particular picture. I was testing my zone tables, and when I tested a relatively large order (for us), the shipping estimator calculated a weight that was only half what the shopping cart main page calculation showed, and assigned a shipping charge that isn't in the zone table at all.

Here's my zone table:

Priority Mail Rates
Enable Zones Method
True
Calculation Method
Weight
Tax Class
--none--
Tax Basis
Shipping
Sort Order
10
Skip Countries, use a comma separated list of the two character ISO country codes

Zone 1 Countries
US
Zone 1 Shipping Table
2.3:5,11:10,30:30,50:50
Zone 1 Handling Fee
0

Zone 2 Countries
CA
Zone 2 Shipping Table
2.3:12,11:25,30:75,50:125
Zone 2 Handling Fee
0

Zone 3 Countries
AU,IE,NZ,GB
Zone 3 Shipping Table
2.3:15,11:40,30:120,50:1000
Zone 3 Handling Fee
0

Zone 4 Countries
00
Zone 4 Shipping Table
2.3:15,11:40,30:120,50:1000
Zone 4 Handling Fee
0

My tare weight settings are 0:0.

The order was 35 copies of a product where the product weight is 1.6 (I assume it thinks this is pounds. All my 1-2 copy tests operated as if this were pounds). The order was placed by a test user in Zone 1.

The shopping cart estimator line looked like this (which by the way is correct):

Total Items: 35 Weight: 56lbs Amount: $700.00

The shipping estimator line looked like this (wrong):

Total Items: 35 Weight: 28lbs Amount: $700.00

Available Shipping Methods Rates
Priority Mail Rates (Shipping to US) $60.00
Store Pickup (Walk In) $0.00

The $60 figure carried all the way through to the final order total calculation on the checkout_payment page. Where did it get $60?? There isn't a table entry that even contains the value $60, for any zone! Help?

[hedera]

I've since realized that the error described in my original post is related to the fact that the weight of the order was OVER the top weight limit in my zone table. The shipping calculations within the limits of the zone table are correct.

I'd still like to know:

Why the shipping estimator calculated only half the weight?
Where the shipping estimate came from?

Any help??