Hi Gunnar,
it does occur with 5.0.0.Final as well.

My EL dependencies were slightly different from the ones mentioned in the ref doc.
However, I've tried with the ones in the Hibernate Validator ref doc and it didn't help.

Also, I tried to run an embedded version of Tomcat (using the dependencies declared in the ref doc) and had an error even on Tomcat 7:

java.lang.LinkageError: loader constraint violation: when resolving interface method "javax.servlet.jsp.JspApplicationContext.getExpressionFactory()Ljavax/el/ExpressionFactory;" the class loader (instance of org/apache/jasper/servlet/JasperLoader) of the current class, org/apache/jsp/WEB_002dINF/jsp/welcome_jsp, and the class loader (instance of org/codehaus/plexus/classworlds/realm/ClassRealm) for resolved class, javax/servlet/jsp/JspApplicationContext, have different Class objects for the type javax/el/ExpressionFactory used in the signature
	org.apache.jsp.WEB_002dINF.jsp.welcome_jsp._jspInit(welcome_jsp.java:36)
	org.apache.jasper.runtime.HttpJspBase.init(HttpJspBase.java:49)

I've created a branch in case you'd like to have a look.
Steps to reproduce:

git clone https://github.com/SpringSource/spring-petclinic/tree/hibernate-validator-el-issue.git
cd spring-petclinic
mvn tomcat7:run

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