FTR, the build scripts attempt to run the enhancer against all entity classes except those that start with 'Unenhanced'.
This fact is probably unrelated to this JIRA issue, which was probably filed because OpenJPA should ideally not be running the enhancer at all in certain configurations. But, if you are looking for a way to store a class that should fail to enhance, then you can name it 'Unenhanced<Something>'.
Also, note that I imagine it'll be a bit tricky to decouple the enhancer in an optimal way. I believe that the -Dtest=false thing is a bit of a hack (recall that you can also do -Dtest=MyTestClassName), so probably has nothing to do with mvn build phases.