Scheduled publication with multiple documents sometimes results in NPE

To reproduce I did the following:
1. create 10 documents
2. schedule publication for each document separately, using the exact same publication time for each document

expected: all documents are published
actual: only 8 documents were published

In the console the following exceptions appear:

CMS 2010-07-16 11:36:00,445 ERROR [org.quartz.core.QuartzSchedulerThread] quartzSchedulerThreadLoop: RuntimeException null
java.lang.NullPointerException
at org.hippoecm.repository.jackrabbit.HippoLocalItemStateManager.update(HippoLocalItemStateManager.java:229)
at org.apache.jackrabbit.core.state.LocalItemStateManager.update(LocalItemStateManager.java:330)
at org.hippoecm.repository.jackrabbit.HippoLocalItemStateManager.update(HippoLocalItemStateManager.java:235)
at org.apache.jackrabbit.core.state.SessionItemStateManager.update(SessionItemStateManager.java:313)
at org.apache.jackrabbit.core.ItemImpl.save(ItemImpl.java:1103)
at org.hippoecm.repository.decorating.ItemDecorator.save(ItemDecorator.java:144)
at org.hippoecm.repository.impl.NodeDecorator.save(NodeDecorator.java:84)
at org.hippoecm.repository.quartz.JCRJobStore.acquireNextTrigger(JCRJobStore.java:384)