I tried as Andreas suggested, also logging the parameter to make sure it is set, the problem persists.
Tomcat usually warns when there are ThreadLocal leaks, no warnings though.
I believe some static field is holding references to loaded classes.
Looking at the memory dump, I see several logging classes instances.
Always 65 instances of org.hibernate.internal.CoreMessageLogger_$logger are alive, this should give some clue about the problem.