My graphs are being affected by this as well - they show everything as 'fixed' when a build fails; these exceptions show up in my jenkins log:

INFO: Loaded data file /var/lib/jenkins/jobs/anonymous.repo/builds/2011-05-05_15-19-23/analysis.xml for build 14
May 5, 2011 6:22:18 PM hudson.ExpressionFactory2$JexlExpression evaluate
WARNING: Caught exception evaluating: it.getStats(job). Reason: java.lang.NullPointerException
java.lang.NullPointerException
at hudson.plugins.projectstats.NumBuildsStatsBuilder.<init>(NumBuildsStatsBuilder.java:25)

....

May 5, 2011 6:22:18 PM hudson.ExpressionFactory2$JexlExpression evaluate
WARNING: Caught exception evaluating: it.getStats(job). Reason: java.lang.NullPointerException
java.lang.NullPointerException
at hudson.plugins.projectstats.NumBuildsStatsBuilder.<init>(NumBuildsStatsBuilder.java:25)

....

Attached is a full dump