Week of coding effort wasted after a successful demo

I was asked to design a data import tool (trivial ETL) and a web-UI with two views for browsing the data. Even though the problem was solved to 100%, and I had caught all the "gotchas" in advance, and demoed and explained the design and implementation details, I received no offer. The interviewers were sending very positive messages starting the phone screening coding problem, as well as during the onsite demo-and-skills probing session. This, however, turned out to be either very fake or hypocritical, as in "assessment against hidden criteria."

I don't recommend anyone spend even an hour on the home assignment. This company is essentially prototyping and stealing your code.

Home coding project assignment (ETL + Web UI + Web Service)