When starting Jenkins, it always happen that a Slave disappears. The node is simply vanished.
I have tried looking for specific errors in the log without success, even looking at all log levels. There is an error while unmarshalling an xml, but unsure if it is related. See the stack trace below in any case.

I have to note that only one disappears, not all.

The curious thing comes that if I click "Reload configuration from disk", the disappeared slave is loaded correctly this time (the configuration was in the xml there all along, and I'm not overwriting it).

Information about my instance:
Version: 1.547 (happened with 1.532 as well)
java.vm.info JRE 1.6.0 IBM J9 2.4 Windows Server 2008 R2 amd64-64 jvmwa6460sr15-20131016_170922 (JIT enabled, AOT enabled)>J9VM - 20131016_170922>JIT - r9_20130920_46510ifx2>GC - GA24_Java6_SR15_20131016_1337_B170922 (happened with an older version as well, tried updating. I'm aware that IBM Java is not officially supported).
Using tomcat 6.0.32, on a windows 2008 R2 Standard.

Possible related bug: https://issues.jenkins-ci.org/browse/JENKINS-21867
(Also on Windows 2008)

Error that might be related:
FINE hudson.util.RobustReflectionConverter addErrorInContext
Failed to load
java.lang.IncompatibleClassChangeError: incompatible InnerClasses attribute between "hudson.model.Queue$ItemList" and "hudson.model.Queue"
at java.lang.Class.getDeclaringClass(Class.java:781)
at sun.reflect.generics.reflectiveObjects.ParameterizedTypeImpl.<init>(ParameterizedTypeImpl.java:46)
at sun.reflect.generics.reflectiveObjects.ParameterizedTypeImpl.make(ParameterizedTypeImpl.java:89)
at sun.reflect.generics.factory.CoreReflectionFactory.makeParameterizedType(CoreReflectionFactory.java:98)
at sun.reflect.generics.visitor.Reifier.visitClassTypeSignature(Reifier.java:134)
at sun.reflect.generics.tree.ClassTypeSignature.accept(ClassTypeSignature.java:43)
at sun.reflect.generics.repository.FieldRepository.getGenericType(FieldRepository.java:79)
at java.lang.reflect.Field.getGenericType(Field.java:236)
at com.thoughtworks.xstream.mapper.AnnotationMapper.processTypes(AnnotationMapper.java:207)
at com.thoughtworks.xstream.mapper.AnnotationMapper.processAnnotations(AnnotationMapper.java:165)
at com.thoughtworks.xstream.mapper.AnnotationMapper.defaultImplementationOf(AnnotationMapper.java:122)
at hudson.util.xstream.MapperDelegate.defaultImplementationOf(MapperDelegate.java:59)
at com.thoughtworks.xstream.mapper.MapperWrapper.defaultImplementationOf(MapperWrapper.java:46)
at com.thoughtworks.xstream.core.TreeUnmarshaller.convertAnother(TreeUnmarshaller.java:54)
at com.thoughtworks.xstream.core.TreeUnmarshaller.convertAnother(TreeUnmarshaller.java:50)
at com.thoughtworks.xstream.converters.collections.AbstractCollectionConverter.readItem(AbstractCollectionConverter.java:71)
at hudson.util.RobustCollectionConverter.populateCollection(RobustCollectionConverter.java:83)
at com.thoughtworks.xstream.converters.collections.CollectionConverter.unmarshal(CollectionConverter.java:61)
at hudson.util.RobustCollectionConverter.unmarshal(RobustCollectionConverter.java:74)
at hudson.slaves.NodeList$ConverterImpl.unmarshal(NodeList.java:162)
at hudson.util.XStream2$AssociatedConverterImpl.unmarshal(XStream2.java:338)
at com.thoughtworks.xstream.core.TreeUnmarshaller.convert(TreeUnmarshaller.java:72)
at com.thoughtworks.xstream.core.AbstractReferenceUnmarshaller.convert(AbstractReferenceUnmarshaller.java:65)
at com.thoughtworks.xstream.core.TreeUnmarshaller.convertAnother(TreeUnmarshaller.java:66)
at hudson.util.RobustReflectionConverter.unmarshalField(RobustReflectionConverter.java:328)
at hudson.util.RobustReflectionConverter.doUnmarshal(RobustReflectionConverter.java:274)
at hudson.util.RobustReflectionConverter.unmarshal(RobustReflectionConverter.java:221)
at com.thoughtworks.xstream.core.TreeUnmarshaller.convert(TreeUnmarshaller.java:72)
at com.thoughtworks.xstream.core.AbstractReferenceUnmarshaller.convert(AbstractReferenceUnmarshaller.java:65)
at com.thoughtworks.xstream.core.TreeUnmarshaller.convertAnother(TreeUnmarshaller.java:66)
at com.thoughtworks.xstream.core.TreeUnmarshaller.convertAnother(TreeUnmarshaller.java:50)
at com.thoughtworks.xstream.core.TreeUnmarshaller.start(TreeUnmarshaller.java:134)
at com.thoughtworks.xstream.core.AbstractTreeMarshallingStrategy.unmarshal(AbstractTreeMarshallingStrategy.java:32)
at com.thoughtworks.xstream.XStream.unmarshal(XStream.java:1061)
at hudson.util.XStream2.unmarshal(XStream2.java:109)
at com.thoughtworks.xstream.XStream.unmarshal(XStream.java:1045)
at hudson.XmlFile.unmarshal(XmlFile.java:163)
at jenkins.model.Jenkins$17.run(Jenkins.java:2545)
at org.jvnet.hudson.reactor.TaskGraphBuilder$TaskImpl.run(TaskGraphBuilder.java:169)
at org.jvnet.hudson.reactor.Reactor.runTask(Reactor.java:282)
at jenkins.model.Jenkins$7.runTask(Jenkins.java:899)
at org.jvnet.hudson.reactor.Reactor$2.run(Reactor.java:210)
at org.jvnet.hudson.reactor.Reactor$Node.run(Reactor.java:117)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:906)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:929)
at java.lang.Thread.run(Thread.java:761)