java - jetty dependencies (classes) not found on server start

Question

I have a WTP project in eclipse and deploy it as a WAR file in jetty 8.1.5. In the /WEB-INF/lib directory there are some dependencies (jars) required for the web application. When I deploy the WAR and start the server I get lots of exceptions about classes which are not found. These classes are available in the jetty jars in /jetty-home/lib If I put these jetty jars in /WEB-INF/lib of the web app, it works fine although as I understand it should not be done that way. what could be the reason??

This is a sample of the exceptions' trace:

java.lang.NoClassDefFoundError: org/eclipse/jetty/util/component/AbstractLifeCycle
    at java.lang.ClassLoader.defineClass1(Native Method)
    at java.lang.ClassLoader.defineClass(Unknown Source)
    at java.security.SecureClassLoader.defineClass(Unknown Source)
    at java.net.URLClassLoader.defineClass(Unknown Source)
    at java.net.URLClassLoader.access$100(Unknown Source)
    at java.net.URLClassLoader$1.run(Unknown Source)
    at java.net.URLClassLoader$1.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(Unknown Source)
    at org.eclipse.jetty.webapp.WebAppClassLoader.loadClass(WebAppClassLoader.java:415)
    at org.eclipse.jetty.webapp.WebAppClassLoader.loadClass(WebAppClassLoader.java:377)
    at java.lang.Class.getDeclaredMethods0(Native Method)
    at java.lang.Class.privateGetDeclaredMethods(Unknown Source)
    at java.lang.Class.getDeclaredMethods(Unknown Source)
    at org.eclipse.jetty.annotations.ResourceAnnotationHandler.doHandle(ResourceAnnotationHandler.java:58)
    at org.eclipse.jetty.annotations.AnnotationIntrospector$AbstractIntrospectableAnnotationHandler.handle(AnnotationIntrospector.java:66)
    at org.eclipse.jetty.annotations.AnnotationIntrospector.introspect(AnnotationIntrospector.java:91)
    at org.eclipse.jetty.annotations.AnnotationDecorator.introspect(AnnotationDecorator.java:158)
    at org.eclipse.jetty.annotations.AnnotationDecorator.decorateServletInstance(AnnotationDecorator.java:110)
    at org.eclipse.jetty.servlet.ServletContextHandler$Context.createServlet(ServletContextHandler.java:1063)
    at org.eclipse.jetty.servlet.ServletHolder.newInstance(ServletHolder.java:916)
    at org.eclipse.jetty.servlet.ServletHolder.initServlet(ServletHolder.java:496)
    at org.eclipse.jetty.servlet.ServletHolder.doStart(ServletHolder.java:326)
    at org.eclipse.jetty.util.component.AbstractLifeCycle.start(AbstractLifeCycle.java:59)
    at org.eclipse.jetty.servlet.ServletHandler.initialize(ServletHandler.java:742)
    at org.eclipse.jetty.servlet.ServletContextHandler.startContext(ServletContextHandler.java:258)
    at org.eclipse.jetty.webapp.WebAppContext.startContext(WebAppContext.java:1233)
    at org.eclipse.jetty.server.handler.ContextHandler.doStart(ContextHandler.java:701)
    at org.eclipse.jetty.webapp.WebAppContext.doStart(WebAppContext.java:475)
    at org.eclipse.jetty.util.component.AbstractLifeCycle.start(AbstractLifeCycle.java:59)
    at org.eclipse.jetty.deploy.bindings.StandardStarter.processBinding(StandardStarter.java:36)
    at org.eclipse.jetty.deploy.AppLifeCycle.runBindings(AppLifeCycle.java:183)
    at org.eclipse.jetty.deploy.DeploymentManager.requestAppGoal(DeploymentManager.java:491)
    at org.eclipse.jetty.deploy.DeploymentManager.addApp(DeploymentManager.java:138)
    at org.eclipse.jetty.deploy.providers.ScanningAppProvider.fileAdded(ScanningAppProvider.java:142)
    at org.eclipse.jetty.deploy.providers.ScanningAppProvider$1.fileAdded(ScanningAppProvider.java:53)
    at org.eclipse.jetty.util.Scanner.reportAddition(Scanner.java:604)
    at org.eclipse.jetty.util.Scanner.reportDifferences(Scanner.java:535)
    at org.eclipse.jetty.util.Scanner.scan(Scanner.java:398)
    at org.eclipse.jetty.util.Scanner.doStart(Scanner.java:332)
    at org.eclipse.jetty.util.component.AbstractLifeCycle.start(AbstractLifeCycle.java:59)
    at org.eclipse.jetty.deploy.providers.ScanningAppProvider.doStart(ScanningAppProvider.java:118)
    at org.eclipse.jetty.util.component.AbstractLifeCycle.start(AbstractLifeCycle.java:59)
    at org.eclipse.jetty.deploy.DeploymentManager.startAppProvider(DeploymentManager.java:552)
    at org.eclipse.jetty.deploy.DeploymentManager.doStart(DeploymentManager.java:227)
    at org.eclipse.jetty.util.component.AbstractLifeCycle.start(AbstractLifeCycle.java:59)
    at org.eclipse.jetty.util.component.AggregateLifeCycle.doStart(AggregateLifeCycle.java:75)
    at org.eclipse.jetty.server.handler.AbstractHandler.doStart(AbstractHandler.java:53)
    at org.eclipse.jetty.server.handler.HandlerWrapper.doStart(HandlerWrapper.java:91)
    at org.eclipse.jetty.server.Server.doStart(Server.java:272)
    at org.eclipse.jetty.util.component.AbstractLifeCycle.start(AbstractLifeCycle.java:59)
    at org.eclipse.jetty.xml.XmlConfiguration$1.run(XmlConfiguration.java:1260)
    at java.security.AccessController.doPrivileged(Native Method)
    at org.eclipse.jetty.xml.XmlConfiguration.main(XmlConfiguration.java:1183)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.eclipse.jetty.start.Main.invokeMain(Main.java:462)
    at org.eclipse.jetty.start.Main.start(Main.java:610)
    at org.eclipse.jetty.start.Main.main(Main.java:86)

When I deploy my web app into another machine (server), I get the following exception:

org.apache.jasper.el.ELContextImpl cannot be cast to org.apache.jasper.runtime.ElContextImpl

and I think it might be related to the jetty jars that I added to /WEB-INF/lib.