I think that if you can attach the entity and/or the hbm.xml, I can then create a test.
I'm probably doing something wrong in my test: https://github.com/DavideD/hibernate-search/commit/1e3aedd040ba339e4c98d90e905e71bc2200bea5

Note that it's not a real test, at the moment I'm just using it to debug and see if the problem occurs.
I will change it as soon as I'm able to recreate the issue.