User Management in Web Manager Portal is broken

It is not possible to show exiting users (list is empty):

And it is not possible to add new users (because the drop-down for roles has no entries):

The logfile shows message like this:

org.springframework.transaction.IllegalTransactionStateException: Pre-bound JDBC Connection found! JpaTransactionManager does not support running within DataSourceTransactionManager if told to manage the DataSource itself. It is recommended to use a single JpaTransactionManager for all transactions on a single DataSource, no matter whether JPA or JDBC access.

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