After upgrade to 1.529 from 1.523, the Maven jobs aren't loaded correctly.
Downgrade back solves it. All the other types of jobs are still visible.

The Maven plugin version doesn't change this behavior.

Failed Loading job BT_Nightly
hudson.util.IOException2: Unable to read /home/.../jobs/.../config.xml
at hudson.XmlFile.read(XmlFile.java:149)
at hudson.model.Items.load(Items.java:220)
at jenkins.model.Jenkins$18.run(Jenkins.java:2553)
at org.jvnet.hudson.reactor.TaskGraphBuilder$TaskImpl.run(TaskGraphBuilder.java:146)
at org.jvnet.hudson.reactor.Reactor.runTask(Reactor.java:259)
at jenkins.model.Jenkins$7.runTask(Jenkins.java:895)
at org.jvnet.hudson.reactor.Reactor$2.run(Reactor.java:187)
at org.jvnet.hudson.reactor.Reactor$Node.run(Reactor.java:94)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:662)
Caused by: java.lang.NoClassDefFoundError: Could not initialize class hudson.maven.MavenModuleSet
at sun.reflect.GeneratedSerializationConstructorAccessor73.newInstance(Unknown Source)
at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
at com.thoughtworks.xstream.converters.reflection.Sun14ReflectionProvider.newInstance(Sun14ReflectionProvider.java:76)
at hudson.util.RobustReflectionConverter.instantiateNewInstance(RobustReflectionConverter.java:376)
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 com.thoughtworks.xstream.XStream.fromXML(XStream.java:925)
at hudson.XmlFile.read(XmlFile.java:143)
}}