I would expect this to fail as well:
acme.jar
* META-INF
** foo-jboss-beans.xml
** foo-service.xml
This actually works due to the fact, that parent deployment unit actually holds "grouped" metadata.
e.g. KernelDeployment for BMDs and ServiceDeployment for SMDs
Hence no BMD or SMD attachment is found in parent dpeloyment unit.
Where we would pick top deployment's SMD or BMD attachment in which ever component deployer would be the one to see 2 component deployment units.
It would pick up the parent's attachement which would be also processed as part of component attachment.
What will make it fail is if we directly put BMD or SMD into deployment unit, which is then the parent of component deployment unit.
Which is what RARDeployer and AppNamingDeployer do.