Observed with Tomcat 5. Get a web facet with some JSP / JSPX. Turn JSP validation on compilation Off. Provide run (deploy) configuration. Run to deploy. Now invoke validation for some deployed JSP. It is done and you get the prompt "Deploy modules ... ?" Say No. Result: facet is undeployed. Following http requests to the application lead to 404 error. I understand that this is a side effect of compilation. But it seems to be not very convenient. The command to validate a JSP is not the same as command to undeploy it.