App Engine doesn't find WEB-INF in WAR created by sbt

Question

I'm trying to make a Lift app that I can run on App Engine and am managing the project with sbt. I have web.xml and appengine-web.xml in src/main/webapp/WEB-INF and package the project with sbt project. According to a previous SO quesiton, that should be all I need. However, I get this:

$ dev_appserver.sh target/scala_2.8.1/
2011-02-06 13:37:45.763 java[20355:903] [Java CocoaComponent compatibility mode]: Enabled
2011-02-06 13:37:45.765 java[20355:903] [Java CocoaComponent compatibility mode]: Setting timeout for SWT to 0.100000
Feb 6, 2011 12:37:47 PM com.google.apphosting.utils.jetty.JettyLogger info
INFO: Logging to JettyLogger(null) via com.google.apphosting.utils.jetty.JettyLogger
com.google.apphosting.utils.config.AppEngineConfigException: Supplied application has to contain WEB-INF directory.
    at com.google.appengine.tools.development.JettyContainerService.determineAppRoot(JettyContainerService.java:319)
    at com.google.appengine.tools.development.JettyContainerService.initContext(JettyContainerService.java:145)
    at com.google.appengine.tools.development.AbstractContainerService.startup(AbstractContainerService.java:146)
    at com.google.appengine.tools.development.DevAppServerImpl.start(DevAppServerImpl.java:219)
    at com.google.appengine.tools.development.DevAppServerMain$StartAction.apply(DevAppServerMain.java:164)
    at com.google.appengine.tools.util.Parser$ParseResult.applyArgs(Parser.java:48)
    at com.google.appengine.tools.development.DevAppServerMain.<init>(DevAppServerMain.java:113)
    at com.google.appengine.tools.development.DevAppServerMain.main(DevAppServerMain.java:89)

Any ideas why? Thanks.