Task Listener bean resolution broken on complete event

I'm using a task listener bean on a user task. I have declared the bean as a Spring bean. In the IDE, I use the Delegate Expression column to 'wire up' the bean to events eg ${genericListener}. This seems to work fine for assign and create events, however on the complete event, I get an exception thrown by the engine...

Jul 14, 2013 10:04:17 AM org.camunda.bpm.engine.rest.exception.ExceptionHandler
toResponse
WARNING: org.camunda.bpm.engine.ProcessEngineException: Exception while invoking
TaskListener: Unknown property used in expression: ${genericListener}. Cause: C
annot resolve identifier 'genericListener'
at org.camunda.bpm.engine.impl.persistence.entity.TaskEntity.fireEvent(T
askEntity.java:573)
at org.camunda.bpm.engine.impl.persistence.entity.TaskEntity.complete(Ta
skEntity.java:157)
at org.camunda.bpm.engine.impl.cmd.CompleteTaskCmd.completeTask(Complete
TaskCmd.java:62)
at org.camunda.bpm.engine.impl.cmd.CompleteTaskCmd.execute(CompleteTaskC
md.java:56)
at org.camunda.bpm.engine.impl.cmd.CompleteTaskCmd.execute(CompleteTaskC
md.java:27)
at org.camunda.bpm.engine.impl.interceptor.CommandExecutorImpl.execute(C
ommandExecutorImpl.java:24)
at org.camunda.bpm.engine.impl.interceptor.CommandContextInterceptor.exe
cute(CommandContextInterceptor.java:42)
at org.camunda.bpm.engine.impl.interceptor.LogInterceptor.execute(LogInt
erceptor.java:32)