"Invalid date input format: [undefined xx:xx:xx]" error by building a package in JBoss BRMS 5.3.x

Issue

After performing some changes in some rules, we are getting the following exception:

ERROR 25-10 08:47:21,802 (LoggingHelper.java:error:74)   Service method 'public abstract org.drools.guvnor.client.rpc.BuilderResult org.drools.guvnor.client.rpc.PackageService.buildPackage(java.lang.String,boolean,java.lang.String,java.lang.String,java.lang.String,boolean,java.lang.String,java.lang.String,boolean,java.lang.String) throws com.google.gwt.user.client.rpc.SerializationException' threw an unexpected exception: java.lang.IllegalArgumentException: Invalid date input format: [undefined 23:59:59] it should follow: [yyyy-MM-dd hh:mm:ss]
java.lang.IllegalArgumentException: Invalid date input format: [undefined 23:59:59] it should follow: [yyyy-MM-dd hh:mm:ss]
    at org.drools.core.util.DateUtils.parseDate(DateUtils.java:73)
...

We are using a different dateformat in $JBOSS_HOME/server/$PROFILE/deploy/jboss-brms.war/WEB-INF/classes/preferences.properties.