设置如下：
cuba.web.mainTabSheetMode = MANAGED
cuba.web.managedMainTabSheetMode = UNLOAD_TABS
在主菜单打开一个之前打开过的界面，直接报错如下：
上面是主菜单里点击“用户”出现的错误，正常情况下应该会自动选中用户这个标签页（因为之前已经打开了）。但是改了cuba.web.mainTabSheetMode后并设置为UNLOAD_TABS就出这个问题了。用户手动切换标签页没有任何问题，只是点菜单的时候出错。
按文档描述：
设置
cuba.web.mainTabSheetMode = MANAGED
cuba.web.managedMainTabSheetMode = UNLOAD_TABS
应该等效于cuba.web.mainTabSheetMode=DEFAULT，且可以由用户去控制特定的Screen不卸载。
感觉是一个严重的BUG。
用的是7.2.10
错误堆栈如下：
java.lang.IllegalStateException: Screen is not opened sec$User.browse
at com.haulmont.cuba.web.sys.WebScreens.checkOpened(WebScreens.java:578)
at com.haulmont.cuba.web.sys.WebScreens.remove(WebScreens.java:648)
at com.haulmont.cuba.gui.screen.Screen.close(Screen.java:340)
at com.haulmont.cuba.web.sys.WebScreens.showFromNavigation(WebScreens.java:540)
at com.haulmont.cuba.gui.config.MenuItemCommands$ScreenCommand.run(MenuItemCommands.java:338)
at com.haulmont.cuba.web.sys.SideMenuBuilder$MenuCommandExecutor.accept(SideMenuBuilder.java:264)
at com.haulmont.cuba.web.sys.SideMenuBuilder$MenuCommandExecutor.accept(SideMenuBuilder.java:249)
at com.haulmont.cuba.web.gui.components.mainwindow.WebSideMenu$MenuItemImpl.menuSelected(WebSideMenu.java:576)
at com.haulmont.cuba.web.widgets.CubaSideMenu$1.menuItemTriggered(CubaSideMenu.java:90)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at com.vaadin.server.ServerRpcManager.applyInvocation(ServerRpcManager.java:153)
at com.vaadin.server.ServerRpcManager.applyInvocation(ServerRpcManager.java:115)
at com.vaadin.server.communication.ServerRpcHandler.handleInvocation(ServerRpcHandler.java:431)
at com.vaadin.server.communication.ServerRpcHandler.handleInvocations(ServerRpcHandler.java:396)
at com.vaadin.server.communication.ServerRpcHandler.handleRpc(ServerRpcHandler.java:260)
at com.vaadin.server.communication.UidlRequestHandler.synchronizedHandleRequest(UidlRequestHandler.java:82)
at com.vaadin.server.SynchronizedRequestHandler.handleRequest(SynchronizedRequestHandler.java:40)
at com.vaadin.server.VaadinService.handleRequest(VaadinService.java:1578)
at com.vaadin.server.VaadinServlet.service(VaadinServlet.java:425)
at com.haulmont.cuba.web.sys.CubaApplicationServlet.serviceAppRequest(CubaApplicationServlet.java:329)
at com.haulmont.cuba.web.sys.CubaApplicationServlet.service(CubaApplicationServlet.java:215)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:733)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.springframework.web.filter.CompositeFilter$VirtualFilterChain.doFilter(CompositeFilter.java:108)
at org.springframework.web.filter.CompositeFilter.doFilter(CompositeFilter.java:74)
at com.haulmont.cuba.web.sys.CubaHttpFilter.doFilter(CubaHttpFilter.java:93)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:97)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:143)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:690)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:78)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:374)
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1590)
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:748)
这是一个已知问题，我们已经反馈了，应该会在7.2.11 中修复。
好的，谢谢，坐等11
