Cannot remove section with several pages in Portfolio

**RedScreen** Removing a detached instance org.olat.modules.portfolio.model.PageImpl#738
link_0 org.olat.core.gui.components.link.Link n/a org.olat.core.gui.control.Event
link_0 com:link_0,org.olat.core.gui.control.Event@be46a54a
 org.olat.core.gui.control.generic.modal.DialogBoxController
 org.olat.modules.portfolio.ui.TableOfContentController
 org.olat.modules.portfolio.ui.BinderController
 org.olat.modules.portfolio.ui.BinderListController
 org.olat.modules.portfolio.ui.PortfolioHomeController
 org.olat.modules.portfolio.ui.PortfolioPersonalToolController
 org.olat.home.HomeMainController
 org.olat.core.commons.fullWebApp.BaseFullWebappController

Cause: stack of 1.cause::org.olat.core.logging.OLATRuntimeException: Removing a detached instance org.olat.modules.portfolio.model.PageImpl#738
-> at org.olat.core.gui.exception.ExceptionWindowController.(ExceptionWindowController.java:116)
   at org.olat.core.gui.exception.MsgFactory.createMessageChiefController(MsgFactory.java:57)
   at org.olat.core.gui.exception.MsgFactory.createMessageChiefController(MsgFactory.java:46)
   at org.olat.core.gui.components.Window.dispatchRequest(Window.java:558)
   at org.olat.core.gui.components.Window.doDispatchRequest(Window.java:251)
   at org.olat.core.gui.components.AbstractComponent.dispatchRequest(AbstractComponent.java:193)
   at org.olat.dispatcher.AuthenticatedDispatcher.processValidDispatchURI(AuthenticatedDispatcher.java:273)
   at org.olat.dispatcher.AuthenticatedDispatcher.execute(AuthenticatedDispatcher.java:190)
   at org.olat.core.servlets.OpenOLATServlet.executeUserRequest(OpenOLATServlet.java:292)
   at org.olat.core.servlets.OpenOLATServlet.doPost(OpenOLATServlet.java:235)
   at javax.servlet.http.HttpServlet.service(HttpServlet.java:661)
stack of 2.cause::java.lang.IllegalArgumentException: Removing a detached instance org.olat.modules.portfolio.model.PageImpl#738
-> at org.hibernate.jpa.event.internal.core.JpaDeleteEventListener.performDetachedEntityDeletionCheck(JpaDeleteEventListener.java:52)
   at org.hibernate.event.internal.DefaultDeleteEventListener.onDelete(DefaultDeleteEventListener.java:89)
   at org.hibernate.internal.SessionImpl.fireDelete(SessionImpl.java:1006)
   at org.hibernate.internal.SessionImpl.delete(SessionImpl.java:936)
   at org.hibernate.engine.spi.CascadingActions$1.cascade(CascadingActions.java:57)
   at org.hibernate.engine.internal.Cascade.cascadeToOne(Cascade.java:391)
   at org.hibernate.engine.internal.Cascade.cascadeAssociation(Cascade.java:316)
   at org.hibernate.engine.internal.Cascade.cascadeProperty(Cascade.java:155)
   at org.hibernate.engine.internal.Cascade.cascadeCollectionElements(Cascade.java:424)
   at org.hibernate.engine.internal.Cascade.cascadeCollection(Cascade.java:356)
   at org.hibernate.engine.internal.Cascade.cascadeAssociation(Cascade.java:319)
2017-05-10 10:11:21,728