org.hibernate.engine.jdbc.internal.JdbcCoordinatorImpl logs "HHH000387: ResultSet's statement was not registered" warnings if it can't find the matching statement for ResultSet. This happens e.g. when connection pool wraps underlying JDBC driver's Statement class with its own Statement proxy. This results in a warning message for each ResultSet. I'm not sure if this causes any behavioral problems other than excessive logging.
At least BoneCP connection pool exhibits this behavior.