You can't share the jbpm jars. Each application must have its own copy since classes like
http://anonsvn.jboss.org/repos/jbpm/jbpm3/tags/jbpm-3.2.6.SP1/modules/core/src/main/java/org/jbpm/instantiation/UserCodeInterceptorConfig.java
use static variables. This is a LARGE issue.
JBoss Seam for example set settings on UserCodeInterceptorConfig and JbpmExpressionEvaluator. These settings will mess will affect ALL applications that share the same class definitions since the settings are a on static variable.