* I uninstalled Kindle from Google Play
* I installed the Amazon Appstore
* I installed Kindle from Amazon Appstore
Direct book purchasing restored.
Every few weeks, the Google Play store uninstalls Kindle from the Amazon Appstore and installs its version.
Being able to use multiple app stores is (imo) Android's primary appeal. If Google Play can arbitrarily replace apps with its own, that's a serious problem.
How do I stop this from happening?
I have verified this -- when it happens, going to Amazon Appstore -> My Apps lists Kindle (Not from Amazon).