While trying to upgrade content from namespace A to namespace B an ItemExistsException: Same name siblings are not allowed is thrown

While trying to move nodes from namespace A to namespace B all children of a certain node need to be moved as well. Performing this action itself seems to be fine, but when the UpdaterEngine performs a commit the migration process fails with the following exception.

CMS 2010-01-13 16:26:57,338 DEBUG [nl.myproject.update.modules.MyProjectUpgrader] ----------------------------------------------------------------------
CMS 2010-01-13 16:26:57,338 DEBUG [nl.myproject.update.modules.MyProjectUpgrader] Updating node of type: myproject:imageset on path: /content/gallery/images/vb-00-someimage.jpg/vb-00-someimage.jpg
CMS 2010-01-13 16:26:57,340 DEBUG [nl.myproject.update.modules.MyProjectUpgrader] Changing primaryNodeType of node: /content/gallery/images/vb-00-someimage.jpg/vb-00-someimage.jpg
CMS 2010-01-13 16:26:57,340 DEBUG [nl.myproject.update.modules.MyProjectUpgrader] Changing namespaceprefix of childnode: /content/gallery/images/vb-00-someimage.jpg/vb-00-someimage.jpg/myproject:thumbnail to: imageset:thumbnail
CMS 2010-01-13 16:26:57,341 DEBUG [nl.myproject.update.modules.MyProjectUpgrader] Changing namespaceprefix of childnode: /content/gallery/images/vb-00-someimage.jpg/vb-00-someimage.jpg/myproject:picture to: imageset:picture
CMS 2010-01-13 16:26:57,341 DEBUG [nl.myproject.update.modules.MyProjectUpgrader] Changing namespaceprefix of property: myproject:robotrunid to: imageset:robotrunid
CMS 2010-01-13 16:26:57,341 DEBUG [nl.myproject.update.modules.MyProjectUpgrader] Changing namespaceprefix of property: myproject:importedsourceid to: imageset:importedsourceid
CMS 2010-01-13 16:26:57,341 DEBUG [nl.myproject.update.modules.MyProjectUpgrader] Changing namespaceprefix of property: myproject:caption to: imageset:caption
CMS 2010-01-13 16:26:57,341 DEBUG [nl.myproject.update.modules.MyProjectUpgrader] Changing namespaceprefix of property: myproject:tooltip to: imageset:tooltip
CMS 2010-01-13 16:26:57,341 DEBUG [nl.myproject.update.modules.MyProjectUpgrader] Changing namespaceprefix of property: myproject:alt to: imageset:alt

CMS 2010-01-13 16:26:57,455 INFO [org.hippoecm.repository.updater.UpdaterEngine] upgrade cycle traverse process commit
CMS 2010-01-13 16:26:58,700 ERROR [org.hippoecm.repository.updater.UpdaterEngine] error in migration cycle: javax.jcr.ItemExistsException: Same name siblings are not allowed: node /content/gallery/images/vb-00-someimage.jpg/vb-00-someimage.jpg[2]/imageset:thumbnail
javax.jcr.ItemExistsException: Same name siblings are not allowed: node /content/gallery/images/vb-00-someimage.jpg/vb-00-someimage.jpg[2]/imageset:thumbnail
at org.apache.jackrabbit.core.SessionImpl.move(SessionImpl.java:979)
at org.hippoecm.repository.decorating.SessionDecorator.move(SessionDecorator.java:194)
at org.hippoecm.repository.updater.UpdaterNode.commit(UpdaterNode.java:262)
at org.hippoecm.repository.updater.UpdaterNode.commit(UpdaterNode.java:346)
at org.hippoecm.repository.updater.UpdaterNode.commit(UpdaterNode.java:346)
at org.hippoecm.repository.updater.UpdaterNode.commit(UpdaterNode.java:346)
at org.hippoecm.repository.updater.UpdaterNode.commit(UpdaterNode.java:346)
at org.hippoecm.repository.updater.UpdaterNode.commit(UpdaterNode.java:346)
at org.hippoecm.repository.updater.UpdaterNode.commit(UpdaterNode.java:346)
at org.hippoecm.repository.updater.UpdaterSession.commit(UpdaterSession.java:214)
at org.hippoecm.repository.updater.UpdaterEngine.upgrade(UpdaterEngine.java:587)
at org.hippoecm.repository.updater.UpdaterEngine.migrate(UpdaterEngine.java:533)
at org.hippoecm.repository.LocalHippoRepository.initializeStartup(LocalHippoRepository.java:330)
at org.hippoecm.repository.LocalHippoRepository.initialize(LocalHippoRepository.java:274)
at org.hippoecm.repository.LocalHippoRepository.<init>(LocalHippoRepository.java:153)
at org.hippoecm.repository.LocalHippoRepository.create(LocalHippoRepository.java:161)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.hippoecm.repository.HippoRepositoryFactory.getHippoRepository(HippoRepositoryFactory.java:238)
at org.hippoecm.repository.RepositoryServlet.init(RepositoryServlet.java:154)