I believe the problem is that the Appspot proxies were crawled, with the client's new homepage content, before Google cached the client's homepage. That was our error by allowing everything but the homepage to be accessed by Appspot. The main Appspot proxies are losing their caches slowly as we corrected the issue quickly. There's 140 Appspot proxies in total that have scraped this client's homepage in the past (before we made changes).
Both backdraft7 and diberry raise interesting points. Why a Google owned proxy is allowed to cache anothers content is disturbing. No panda, penguin or other algorithm should promote the theft of content, but Google's algorithm and lack of noindex use on their proxies presently condones such actions.
In my observation, Google has absolutely no respect for the originator of quality content. If you are one of the lucky ones to already have domain authority, you are free to rip someones elses work for your benefit. You also are probably benefiting from host crowding.
To be fair, I'm not as qualified as a SEO as most on this forum. But I am finding myself doing things that Google says we should not do by developing content for the search engines. If Google would quit allowing the theft of others work with Appspot proxies, and be more aggressive in policing Blogspot scrapers, maybe I and thousands of other webmasters could focus on other tasks.