(I don't know whether it's a bug or a "missing feature"). I have deployed into a Tomcat 5.5.17 a webapp. The jsp-api.jar file was accidentally left into its WEB-INF/lib directory. When launching the server, no complaints are displayed on the screen or logs, but the presence of that jar causes malfunctions (the JSPs are not rendered, and no log or warning messages are displayed). If the servlet-api.jar is left into the webapp, Tomcat displays a warning message. I find strange that a message is not shown in the jsp-api.jar case. Kind regards.
Good suggestion: I've implemented it for the next release. Thank you.