Different authentication behaviour between 1.4.x and 1.5.x :-(

[Thomas Fromm]

Environment: JBoss 4.0.5, Tomcat 5.5 (both have also Liferay portal server 
deployed as separate webapp)

Hi,

recognized a different login-behaviour after updating from 1.4.x to 1.5.x.

I have configured my own LoginModule (the config is the same for both 
versions):
    <Security appName="Jackrabbit">
        <AccessManager 
class="org.apache.jackrabbit.core.security.SimpleAccessManager"/>
        <LoginModule 
class="com.inubit.ibis.server.repository.IBISLoginModule"/>
    </Security>

My own login module works in the following conditions:
Tomcat + Liferay + Jackrabbit 1.4.x
Tomcat + Liferay + Jackrabbit 1.5.x
JBoss + Tomcat + Liferay + Jackrabbit 1.4.x

The configuration is in all cases the same.
For Liferay is a PortalRealm configured using 
-Djava.security.auth.login.config=...
(Also in all cases.)

JBoss + Tomcat + Liferay + Jackrabbit 1.5.x creates following exception:
java.lang.RuntimeException: javax.jcr.LoginException
...
Caused by: javax.jcr.LoginException
        at 
org.apache.jackrabbit.core.RepositoryImpl.login(RepositoryImpl.java:1401)
...
Caused by: javax.security.auth.login.LoginException
        at 
com.liferay.portal.security.jaas.ext.BasicLoginModule.login(BasicLoginModule.java:88)
...

So here are my questions:
1) How can I make sure with Jackrabbit 1.5.x and JBoss, that my login module 
is used?

2) Is it possible to roll-back the Jackrabbit libs to 1.4.x without damaging 
the repository files?

thanks in advance,
--tf