After upgrading from 1.504 to 1.507, all our Matrix jobs are failing to load with this message and NullPointerException:

SEVERE: Failed Loading job BPS 2.4-branch VC++ Matrix
java.lang.NullPointerException
at hudson.matrix.MatrixProject.getItem(MatrixProject.java:669)
at hudson.matrix.MatrixProject.getItem(MatrixProject.java:662)
at hudson.matrix.MatrixProject.getItem(MatrixProject.java:98)
at hudson.model.AbstractProject.onLoad(AbstractProject.java:291)
at hudson.model.Project.onLoad(Project.java:83)
at hudson.matrix.MatrixConfiguration.onLoad(MatrixConfiguration.java:89)
at hudson.matrix.MatrixProject.loadConfigurations(MatrixProject.java:541)
at hudson.matrix.MatrixProject.loadConfigurations(MatrixProject.java:548)
at hudson.matrix.MatrixProject.loadConfigurations(MatrixProject.java:548)
at hudson.matrix.MatrixProject.rebuildConfigurations(MatrixProject.java:585)
at hudson.matrix.MatrixProject.onLoad(MatrixProject.java:476)
at hudson.model.Items.load(Items.java:221)
at jenkins.model.Jenkins$17.run(Jenkins.java:2552)
at org.jvnet.hudson.reactor.TaskGraphBuilder$TaskImpl.run(TaskGraphBuilder.java:146)
at org.jvnet.hudson.reactor.Reactor.runTask(Reactor.java:259)
at jenkins.model.Jenkins$7.runTask(Jenkins.java:887)
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$Worker.runTask(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
25-03-2013 08:38:06 jenkins.InitReactorRunner$1 onTaskFailed

Configuration file attached.