Many warnings in hippo-site log about rendered components

When navigating the site many warnings are logged about rendered components that are not added to the response.
During the concurrency test 10488 such warnings are logged

11.12.2013 15:53:17 WARN [org.hippoecm.hst.core.container.AggregationValve.processWindowsRender():445] Component 'eventform' gets rendered but never adds anything to the response. Component id is 'hst:pages/events-detail/main/right/eventform' and renderer 'jsp/easyforms/formtemplate.jsp' is never flushed to a parent component. This is waste.

11.12.2013 15:53:17 WARN [org.hippoecm.hst.core.container.AggregationValve.processWindowsRender():445] Component 'eventform' gets rendered but never adds anything to the response. Component id is 'hst:pages/events-detail/main/right/eventform' and renderer 'jsp/easyforms/formtemplate.jsp' is never flushed to a parent component. This is waste.

11.12.2013 15:53:18 WARN [org.hippoecm.hst.core.container.AggregationValve.processWindowsRender():445] Component 'left' gets rendered but never adds anything to the response. Component id is 'hst:pages/jobs-detail/main-hst:pages/simplepage/main-hst:pages/standardpage/main/left' and renderer 'jsp/standard/main/left.jsp' is never flushed to a parent component. This is waste.

11.12.2013 15:53:17 WARN [org.hippoecm.hst.core.container.AggregationValve.processWindowsRender():445] Component 'productsfacetnav' gets rendered but never adds anything to the response. Component id is 'hst:pages/homepage/main/productsfacetnav' and renderer 'jsp/home/productsfacetnav.jsp' is never flushed to a parent component. This is waste.