I think I discovered the problem. This was in the POM.
<dependency>
<groupId>com.google.endpoints</groupId>
<artifactId>endpoints-management-control-appengine-all</artifactId>
<version>1.0.14</version>
</dependency>
It seems to work when the version is changed to 1.0.15. I don't quite trust it yet. So, I'll have to work with it for a while longer.