For example when creating dynamic web project and hibernate console (for precise steps see JBIDE-8189) when trying to expand HB CC -> Database for the FIRST TIME there is an HibernateException (see below). After "Rebuild Configuration" everything goes to normal. Exception is not always here but I saw it several times during few days.

org.hibernate.HibernateException: Could not instantiate dialect class
at org.hibernate.dialect.resolver.DialectFactory.constructDialect(DialectFactory.java:163)
at org.hibernate.dialect.resolver.DialectFactory.buildDialect(DialectFactory.java:109)
at org.hibernate.cfg.SettingsFactory.buildSettings(SettingsFactory.java:146)
at org.hibernate.cfg.Configuration.buildSettingsInternal(Configuration.java:2163)
at org.hibernate.cfg.Configuration.buildSettings(Configuration.java:2155)
at org.hibernate.eclipse.console.workbench.LazyDatabaseSchemaWorkbenchAdapter$2.execute(LazyDatabaseSchemaWorkbenchAdapter.java:110)
at org.hibernate.console.execution.DefaultExecutionContext.execute(DefaultExecutionContext.java:63)
at org.hibernate.console.ConsoleConfiguration.execute(ConsoleConfiguration.java:72)
at org.hibernate.eclipse.console.workbench.LazyDatabaseSchemaWorkbenchAdapter.readDatabaseSchema(LazyDatabaseSchemaWorkbenchAdapter.java:107)
at org.hibernate.eclipse.console.workbench.LazyDatabaseSchemaWorkbenchAdapter.getChildren(LazyDatabaseSchemaWorkbenchAdapter.java:63)
at org.hibernate.eclipse.console.workbench.BasicWorkbenchAdapter.fetchDeferredChildren(BasicWorkbenchAdapter.java:106)
at org.eclipse.ui.progress.DeferredTreeContentManager$1.run(DeferredTreeContentManager.java:235)
at org.eclipse.core.internal.jobs.Worker.run(Worker.java:54)
Caused by: java.lang.ClassCastException: org.hibernate.dialect.HSQLDialect cannot be cast to org.hibernate.dialect.Dialect
at org.hibernate.dialect.resolver.DialectFactory.constructDialect(DialectFactory.java:157)
... 12 more

rebuild