The Grails 2.X version of the plugin is also running against Hibernate 4, so you should be able to copy-paste these integration tests to your project too (you'll also need to add the domain classes they use).
If these integration tests uncover bugs then I can probably point you towards a fix, because they all pass when run against the Grails 2 plugin.
I'm a maintainer of the Grails 2 version of this plugin. I recently fixed some very severe bugs and added new integration tests to prevent regressions.
The Grails 2.X version of the plugin is also running against Hibernate 4, so you should be able to copy-paste these integration tests to your project too (you'll also need to add the domain classes they use).
If these integration tests uncover bugs then I can probably point you towards a fix, because they all pass when run against the Grails 2 plugin.