Internal server Error when parsing MediaType string: application/xhtml+xml application/pdf

RestEasy throws java.lang.IllegalArgumentException when processing GET request with ACCEPT mediatype string: "application/xhtml+xml application/pdf":

javax.servlet.ServletException: java.lang.IllegalArgumentException: Failure parsing MediaType string: application/xhtml+xml application/pdf
at org.jboss.seam.servlet.ContextualHttpServletRequest.run(ContextualHttpServletRequest.java:74)
at org.jboss.seam.resteasy.ResteasyResourceAdapter.getResource(ResteasyResourceAdapter.java:121)
at org.jboss.seam.servlet.SeamResourceServlet.service(SeamResourceServlet.java:80)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:847)
at org.apache.catalina.core.ApplicationFilterChain.servletService(ApplicationFilterChain.java:427)
at org.apache.catalina.core.ApplicationDispatcher.doInvoke(ApplicationDispatcher.java:875)
at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:723)
at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:560)
at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:490)
at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:382)
at org.apache.catalina.core.StandardHostValve.custom(StandardHostValve.java:549)
at org.apache.catalina.core.StandardHostValve.status(StandardHostValve.java:438)
at org.apache.catalina.core.StandardHostValve.postInvoke(StandardHostValve.java:249)
at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:649)
at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:593)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:587)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:1096)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:166)
at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:648)
at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:593)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:587)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:1096)
at org.apache.coyote.tomcat5.CoyoteAdapter.service(CoyoteAdapter.java:288)
at com.sun.enterprise.web.connector.grizzly.DefaultProcessorTask.invokeAdapter(DefaultProcessorTask.java:647)
at com.sun.enterprise.web.connector.grizzly.DefaultProcessorTask.doProcess(DefaultProcessorTask.java:579)
at com.sun.enterprise.web.connector.grizzly.DefaultProcessorTask.process(DefaultProcessorTask.java:831)
at com.sun.enterprise.web.connector.grizzly.DefaultReadTask.executeProcessorTask(DefaultReadTask.java:341)
at com.sun.enterprise.web.connector.grizzly.DefaultReadTask.doTask(DefaultReadTask.java:263)
at com.sun.enterprise.web.connector.grizzly.DefaultReadTask.doTask(DefaultReadTask.java:214)
at com.sun.enterprise.web.portunif.PortUnificationPipeline$PUTask.doTask(PortUnificationPipeline.java:380)
at com.sun.enterprise.web.connector.grizzly.TaskBase.run(TaskBase.java:265)
at com.sun.enterprise.web.connector.grizzly.ssl.SSLWorkerThread.run(SSLWorkerThread.java:106)
Caused by: java.lang.IllegalArgumentException: Failure parsing MediaType string: application/xhtml+xml application/pdf
at org.jboss.resteasy.plugins.delegates.MediaTypeHeaderDelegate.parse(MediaTypeHeaderDelegate.java:42)
at org.jboss.resteasy.plugins.delegates.MediaTypeHeaderDelegate.fromString(MediaTypeHeaderDelegate.java:18)
at javax.ws.rs.core.MediaType.valueOf(MediaType.java:226)
at org.jboss.resteasy.util.MediaTypeHelper.parseHeader(MediaTypeHelper.java:204)
at org.jboss.resteasy.plugins.server.servlet.ServletUtil.extractAccepts(ServletUtil.java:119)
at org.jboss.resteasy.plugins.server.servlet.ServletUtil.extractHttpHeaders(ServletUtil.java:82)
at org.jboss.seam.resteasy.ResteasyResourceAdapter$1.process(ResteasyResourceAdapter.java:127)
at org.jboss.seam.servlet.ContextualHttpServletRequest.run(ContextualHttpServletRequest.java:53)
... 31 more

This error occures regularly when processing requests from some WEB-crawlers. It should be "HTTP Error 400 Bad request" instead.