Hi Ben,
Thanks for the quick reply. I had lots of things to do so I couldn't check your solution.
I have tried changing the
Code:
<property name="hibernate.hbm2ddl.auto" value="create"/>
to
Code:
<property name="hibernate.hbm2ddl.auto" value="update"/>
and it works fine, i.e data is preserved between restarts 
But I couldn't find the comments in the persistence.xml file.
To help you with this, Roo automatically lists the valid settings for your JPA provider as a comment in that file.
Am I missing something?