Amazon Ads Overcharging?

Happy (US) Thanksgiving! This post serves as both a question and warning. I've noticed something odd with my Amazon Ads and--so far--Amazon has not offered an explanation. Maybe you can?

I use Amazon Advertising to run paid ads for my ebooks (I ran a post earlier this year if you're interested in how the process works). The problem I'm having is that Amazon appears to be overcharging me for ads.

Now, I'll admit, being only an engineer, my math skills may be sub-par, but indulge my logic, if you will. For each ad you run, Amazon lets you select a default bid (below I have $0.52 set) and allows you to adjust your bid dynamically (I selected a 14% maximum increase). This means that under certain conditions Amazon deems favorable, my $0.52 bid could go as high as $0.59 ($0.52 x 1.14 = $0.59).

However, Amazon also lets you set prices for each individual key word (i.e., search term). As you can see below, my highest individual bid is set at $0.57, which would make my maximum dynamic bid cost $0.65 ($0.57 x 1.14 = $0.65).

Now the problem is, Amazon is charging me more than my maximum bids (as shown below). As you can see, my ad that should cost a maximum of 65 cents is costing me as much as $0.99 (CPC means Cost per Click). This results in an overcharge of 34 cents per click, or almost 40%.

Granted, 34 cents a click is not much at face value, but when you scale up this cost by 1,000 clicks, for example, you find yourself shorted $340. Imagine Amazon overcharging a million customers by 34 cents a click and the numbers get astronomically high very quickly.

Anyhow, I paused all my Amazon ads until this problem gets resolved (if it ever does). If you have any insight with this issue, see a mistake in my math, or have experienced a similar problem, I'm interested in hearing about it. And I'll let you know if Amazon ever gets back to me.