I am observing this with the current Tomcat 7 (built from revision 1605072)
If the following 3 conditions are met:
1) Server is running in "strict compliance" mode
2) There is a servlet that is mapped to context root using URL pattern "" (empty string) - per Servlet 3.0 mrel spec chapter 12.2 Specification of Mappings

Then whenever Tomcat tries to compile a JSP page, it fails when trying to validate effective merged web.xml against the schema.

WORKAROUND:
To work around the issue I disabled XML validation for this specific context, via <Context xmlValidation="false"/>

STEPS TO REPRODUCE:
1. Add the following mapping at the end of webapps/examples/WEB-INF/web.xml:
[[[
    <servlet-mapping>
        <servlet-name>RequestInfoExample</servlet-name>
        <url-pattern />
    </servlet-mapping>
]]]

2. Configure Tomcat in "strict compliance" mode by adding the following line to conf/catalina.properties:
org.apache.catalina.STRICT_SERVLET_COMPLIANCE=true

3. Purge the work/ directory to remove compiled JSPs, if there are any.
4. Start Tomcat

5. Access http://localhost:8080/examples/
The "Request Information Example" page is shown. Thus the empty URL mapping is working correctly.

6. Access a JSP page, http://localhost:8080/examples/jsp/jsp2/el/basic-arithmetic.jsp
Expected: Some arithmetics demo page
Actual: Error 500

HTTP Status 500 - org.apache.jasper.JasperException: XML parsing error on file org.apache.tomcat.util.scan.MergedWebXml: (line 176, col 21)

Stack Trace:
org.apache.jasper.JasperException: org.apache.jasper.JasperException: XML parsing error on file org.apache.tomcat.util.scan.MergedWebXml: (line 176, col 21)
	org.apache.jasper.compiler.JspConfig.processWebDotXml(JspConfig.java:230)
	org.apache.jasper.compiler.JspConfig.init(JspConfig.java:243)
	org.apache.jasper.compiler.JspConfig.findJspProperty(JspConfig.java:302)
	org.apache.jasper.compiler.Compiler.generateJava(Compiler.java:114)
(...)