I have been having some issues with build slaves dropping their SSH connections lately. These cause build failures and extraneous rebuilds. The build failures do not cause a failure e-mail, for some reason:

For example:

...
01:55:14 [proguard] Reading library jar [/opt/WTK2.5.2/lib/jsr179.jar]
02:12:48 ERROR: Failed to parse POMs
02:12:48 hudson.remoting.ChannelClosedException: channel is already closed
02:12:48 at hudson.remoting.Channel.send(Channel.java:494)
02:12:48 at hudson.remoting.Request.call(Request.java:129)
02:12:48 at hudson.remoting.Channel.call(Channel.java:665)
02:12:48 at hudson.remoting.RemoteInvocationHandler.invoke(RemoteInvocationHandler.java:158)
02:12:48 at $Proxy37.isAlive(Unknown Source)
02:12:48 at hudson.Launcher$RemoteLauncher$ProcImpl.isAlive(Launcher.java:920)
02:12:48 at hudson.maven.ProcessCache$MavenProcess.call(ProcessCache.java:161)
02:12:48 at hudson.maven.MavenModuleSetBuild$MavenModuleSetBuildExecution.doRun(MavenModuleSetBuild.java:748)
02:12:48 at hudson.model.AbstractBuild$AbstractBuildExecution.run(AbstractBuild.java:586)
02:12:48 at hudson.model.Run.execute(Run.java:1518)
02:12:48 at hudson.maven.MavenModuleSetBuild.run(MavenModuleSetBuild.java:477)
02:12:48 at hudson.model.ResourceController.execute(ResourceController.java:88)
02:12:48 at hudson.model.Executor.run(Executor.java:236)
02:12:48 Caused by: java.io.IOException: Unexpected termination of the channel
02:12:48 at hudson.remoting.SynchronousCommandTransport$ReaderThread.run(SynchronousCommandTransport.java:50)
02:12:48 Caused by: java.io.EOFException
02:12:48 at java.io.ObjectInputStream$BlockDataInputStream.peekByte(ObjectInputStream.java:2570)
02:12:48 at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1314)
02:12:48 at java.io.ObjectInputStream.readObject(ObjectInputStream.java:368)
02:12:48 at hudson.remoting.Command.readFrom(Command.java:90)
02:12:48 at hudson.remoting.ClassicCommandTransport.read(ClassicCommandTransport.java:59)
02:12:48 at hudson.remoting.SynchronousCommandTransport$ReaderThread.run(SynchronousCommandTransport.java:48)
02:12:48 Looks like the node went offline during the build. Check the slave log for the details.
details

02:12:48 FATAL: channel is already closed
02:12:48 hudson.remoting.ChannelClosedException: channel is already closed
02:12:48 at hudson.remoting.Channel.send(Channel.java:494)
02:12:48 at hudson.remoting.Request.call(Request.java:129)
02:12:48 at hudson.remoting.Channel.call(Channel.java:665)
02:12:48 at hudson.Launcher$RemoteLauncher.kill(Launcher.java:877)
02:12:48 at hudson.model.AbstractBuild$AbstractBuildExecution.run(AbstractBuild.java:609)
02:12:48 at hudson.model.Run.execute(Run.java:1518)
02:12:48 at hudson.maven.MavenModuleSetBuild.run(MavenModuleSetBuild.java:477)
02:12:48 at hudson.model.ResourceController.execute(ResourceController.java:88)
02:12:48 at hudson.model.Executor.run(Executor.java:236)
02:12:48 Caused by: java.io.IOException: Unexpected termination of the channel
02:12:48 at hudson.remoting.SynchronousCommandTransport$ReaderThread.run(SynchronousCommandTransport.java:50)
02:12:48 Caused by: java.io.EOFException
02:12:48 at java.io.ObjectInputStream$BlockDataInputStream.peekByte(ObjectInputStream.java:2570)
02:12:48 at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1314)
02:12:48 at java.io.ObjectInputStream.readObject(ObjectInputStream.java:368)
02:12:48 at hudson.remoting.Command.readFrom(Command.java:90)
02:12:48 at hudson.remoting.ClassicCommandTransport.read(ClassicCommandTransport.java:59)
02:12:48 at hudson.remoting.SynchronousCommandTransport$ReaderThread.run(SynchronousCommandTransport.java:48)