some further investigations/remarks:

for some performance senstivie tasks, we do a lot of parameterized queries where the parameter make use of lists:

typedQuery.setParameter("parameterName", someParameterList);

Unfortunately, the someParameterList is expanded by Hibernate internally before hitting the query cache. Meaning that queries using list parameters neber hit the query cache if the list counts differ (which is probably the most common case). And this results in a new query plan for every query with the above mentioned class loading issue.

=> about 20% to 25% performance decrease