Noun: Foolish or silly behavior
They seem to be doing something like it again today:
In the screenshot the left window is logged in to my account, the right is a private browser (no naughty cookies for Amazon to use to identify me), copy/pasted the URL to both sides to ensure that I’m looking at identical items on both sides.
Note the Kindle price varies from $7.99 to $6.39.
UPDATE: Amazon never did respond. Shame.