RS: The IM roster is not multithread, it's needed as update came from different threads

RedScreen on node8
2013-09-17 08:25:49,210 [ajp-apr-8005-exec-5] ERROR Window - OLAT::ERROR ^% N5-E13 ^% org.olat.core.gui.components
Mozilla/5.0 (Windows NT 6.1; rv:9.0.1) Gecko/20100101 Firefox/9.0.1
*RedScreen* exception while rendering component 'ffo_roster' (org.olat.core.gui.components.velocity.VelocityContainer) listener:[]
Message of exception: exception occured while merging template: null :::: :::: ^%
>>> stack of 1.cause::org.olat.core.logging.OLATRuntimeException: exception while rendering component 'ffo_roster'(org.olat.core.gui.components.velocity.VelocityContainer) listener:[]
Message of exception: exception occured while merging template: null
-> at org.olat.core.gui.components.Window.handleDirties(Window.java:955)
at org.olat.core.gui.components.Window.dispatchRequest(Window.java:437)
at org.olat.core.gui.components.Window.doDispatchRequest(Window.java:226)
at org.olat.core.gui.components.Component.dispatchRequest(Component.java:192)
at org.olat.dispatcher.AuthenticatedDispatcher.execute(AuthenticatedDispatcher.java:227)
at org.olat.core.dispatcher.DispatcherAction.execute(DispatcherAction.java:154)
at org.olat.core.servlets.OLATServlet.doPost(OLATServlet.java:155)
at org.olat.core.servlets.OLATServlet.doGet(OLATServlet.java:128)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
at org.olat.core.servlets.OLATServlet.service(OLATServlet.java:112)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
>>> stack of 2.cause::org.olat.core.logging.OLATRuntimeException: exception occured while merging template: null
-> at org.olat.core.gui.render.velocity.VelocityHelper.merge(VelocityHelper.java:170)
at org.olat.core.gui.render.velocity.VelocityHelper.mergeContent(VelocityHelper.java:183)
at org.olat.core.gui.components.velocity.VelocityContainerRenderer.render(VelocityContainerRenderer.java:76)
at org.olat.core.gui.render.Renderer.render(Renderer.java:257)
at org.olat.core.gui.components.form.flexible.impl.FormWrapperContainerRenderer.render(FormWrapperContainerRenderer.java:120)
at org.olat.core.gui.render.Renderer.render(Renderer.java:257)
at org.olat.core.gui.components.panel.PanelRenderer.render(PanelRenderer.java:65)
at org.olat.core.gui.render.Renderer.render(Renderer.java:257)
at org.olat.core.gui.render.Renderer.render(Renderer.java:189)
at org.olat.core.gui.render.velocity.VelocityRenderDecorator.doRender(VelocityRenderDecorator.java:572)
at org.olat.core.gui.render.velocity.VelocityRenderDecorator.render(VelocityRenderDecorator.java:269)
>>> stack of 3.cause::java.util.ConcurrentModificationException: null
-> at java.util.ArrayList$Itr.checkForComodification(Unknown Source)
at java.util.ArrayList$Itr.next(Unknown Source)
at org.apache.velocity.runtime.directive.Foreach.render(Foreach.java:393)
at org.apache.velocity.runtime.parser.node.ASTDirective.render(ASTDirective.java:207)
at org.apache.velocity.runtime.parser.node.SimpleNode.render(SimpleNode.java:342)
at org.apache.velocity.Template.merge(Template.java:356)
at org.apache.velocity.Template.merge(Template.java:260)
at org.olat.core.gui.render.velocity.VelocityHelper.merge(VelocityHelper.java:165)
at org.olat.core.gui.render.velocity.VelocityHelper.mergeContent(VelocityHelper.java:183)
at org.olat.core.gui.components.velocity.VelocityContainerRenderer.render(VelocityContainerRenderer.java:76)
at org.olat.core.gui.render.Renderer.render(Renderer.java:257)