AbstractMethodError from SCM.poll

I upgraded two Hudson servers, both using latest Mercurial plugin, to Hudson 1.349. One seems fine. On the other one, SCM polling is completely broken (for jobs built either on master or slaves):

Last Mercurial Polling Log

Started on Mar 8, 2010 5:31:08 PM
ERROR: Failed to record SCM polling
[8mha:AAA....<junk>....AAA==[0mjava.lang.AbstractMethodError
at hudson.scm.SCM.poll(SCM.java:344)
at hudson.model.AbstractProject.poll(AbstractProject.java:1149)
at hudson.triggers.SCMTrigger$Runner.runPolling(SCMTrigger.java:319)
at hudson.triggers.SCMTrigger$Runner.run(SCMTrigger.java:348)
at hudson.util.SequentialExecutionQueue$QueueEntry.run(SequentialExecutionQueue.java:118)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:441)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
at java.util.concurrent.FutureTask.run(FutureTask.java:138)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:619)

The stack trace is odd because it looks like it is throwing AME from inside the catch block for AME, calling the older method!