TimerStartEvents of EventSubprocesses can't evaluate timer expressions when started at specific activity

Steps to reproduce

• Create a sample Process with a TimerStartEvent on a EventSubprocess
• TimerStartEvent uses expression for the timer duration, like ${escalationPeriod}
• Process instance is started with timer expression variable (escalationPeriod = "PT1S") at specific activity

   ProcessInstantiationBuilder builder = runtimeService.createProcessInstanceByKey("dyn-timer-sample").setVariable("escalationPeriod", "PT1S");
          builder.startBeforeActivity("DO_SOMETHING"); 

Observed Behaviour

• Process instance starting fails
• The following exception is printed

  org.camunda.bpm.engine.ProcessEngineException: Unknown property used in expression: ${escalationPeriod}. Cause: Cannot resolve identifier 'escalationPeriod'
  	at org.camunda.bpm.engine.impl.el.JuelExpression.getValue(JuelExpression.java:63)
  	at org.camunda.bpm.engine.impl.el.JuelExpression.getValue(JuelExpression.java:51)
  	at org.camunda.bpm.engine.impl.jobexecutor.TimerDeclarationImpl.resolveAndSetDuedate(TimerDeclarationImpl.java:131)
  	at org.camunda.bpm.engine.impl.jobexecutor.TimerDeclarationImpl.initializeConfiguration(TimerDeclarationImpl.java:99)
  	at org.camunda.bpm.engine.impl.jobexecutor.TimerDeclarationImpl.postInitialize(TimerDeclarationImpl.java:158)
  	at org.camunda.bpm.engine.impl.jobexecutor.TimerDeclarationImpl.postInitialize(TimerDeclarationImpl.java:40)
  	at org.camunda.bpm.engine.impl.jobexecutor.JobDeclaration.createJobInstance(JobDeclaration.java:125)
  	at org.camunda.bpm.engine.impl.jobexecutor.TimerDeclarationImpl.createTimer(TimerDeclarationImpl.java:185)
  	at org.camunda.bpm.engine.impl.jobexecutor.TimerDeclarationImpl.createTimerInstance(TimerDeclarationImpl.java:170)
  	at org.camunda.bpm.engine.impl.persistence.entity.ExecutionEntity.createTimerInstances(ExecutionEntity.java:427)
  	at org.camunda.bpm.engine.impl.persistence.entity.ExecutionEntity.initializeTimerDeclarations(ExecutionEntity.java:419)
  	at org.camunda.bpm.engine.impl.pvm.runtime.PvmExecutionImpl.startWithoutExecuting(PvmExecutionImpl.java:297)
  	at org.camunda.bpm.engine.impl.persistence.entity.ExecutionEntity.startWithoutExecuting(ExecutionEntity.java:465)
  	at org.camunda.bpm.engine.impl.cmd.StartProcessInstanceAtActivitiesCmd.execute(StartProcessInstanceAtActivitiesCmd.java:87)
  	at org.camunda.bpm.engine.impl.cmd.StartProcessInstanceAtActivitiesCmd.execute(StartProcessInstanceAtActivitiesCmd.java:50)
  	at org.camunda.bpm.engine.impl.interceptor.CommandExecutorImpl.execute(CommandExecutorImpl.java:28)
  	at org.camunda.bpm.engine.impl.interceptor.CommandContextInterceptor.execute(CommandContextInterceptor.java:110)
  	at org.camunda.bpm.engine.impl.interceptor.ProcessApplicationContextInterceptor.execute(ProcessApplicationContextInterceptor.java:70)
  	at org.camunda.bpm.engine.impl.interceptor.LogInterceptor.execute(LogInterceptor.java:33)
  	at org.camunda.bpm.engine.impl.ProcessInstantiationBuilderImpl.executeWithVariablesInReturn(ProcessInstantiationBuilderImpl.java:166)
  	at org.camunda.bpm.engine.impl.ProcessInstantiationBuilderImpl.execute(ProcessInstantiationBuilderImpl.java:132)
  	at org.camunda.bpm.engine.impl.ProcessInstantiationBuilderImpl.execute(ProcessInstantiationBuilderImpl.java:128)
  	at at.jrap.bpm.plain.DynTimerTest.shortRunFail(DynTimerTest.java:71)
  	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
  	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
  	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
  	at java.lang.reflect.Method.invoke(Method.java:498)
  	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
  	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
  	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
  	at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
  	at org.junit.rules.TestWatcher$1.evaluate(TestWatcher.java:55)
  	at org.camunda.bpm.engine.test.ProcessEngineRule$1.evaluate(ProcessEngineRule.java:172)
  	at org.junit.rules.RunRules.evaluate(RunRules.java:20)
  	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
  	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
  	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
  	at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
  	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
  	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
  	at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
  	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
  	at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
  	at org.apache.maven.surefire.junit4.JUnit4Provider.execute(JUnit4Provider.java:252)
  	at org.apache.maven.surefire.junit4.JUnit4Provider.executeTestSet(JUnit4Provider.java:141)
  	at org.apache.maven.surefire.junit4.JUnit4Provider.invoke(JUnit4Provider.java:112)
  	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
  	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
  	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
  	at java.lang.reflect.Method.invoke(Method.java:498)
  	at org.apache.maven.surefire.util.ReflectionUtils.invokeMethodWithArray(ReflectionUtils.java:189)
  	at org.apache.maven.surefire.booter.ProviderFactory$ProviderProxy.invoke(ProviderFactory.java:165)
  	at org.apache.maven.surefire.booter.ProviderFactory.invokeProvider(ProviderFactory.java:85)
  	at org.apache.maven.surefire.booter.ForkedBooter.runSuitesInProcess(ForkedBooter.java:115)
  	at org.apache.maven.surefire.booter.ForkedBooter.main(ForkedBooter.java:75)
  Caused by: org.camunda.bpm.engine.impl.javax.el.PropertyNotFoundException: Cannot resolve identifier 'escalationPeriod'
  	at org.camunda.bpm.engine.impl.juel.AstIdentifier.eval(AstIdentifier.java:83)
  	at org.camunda.bpm.engine.impl.juel.AstEval.eval(AstEval.java:50)
  	at org.camunda.bpm.engine.impl.juel.AstNode.getValue(AstNode.java:26)
  	at org.camunda.bpm.engine.impl.juel.TreeValueExpression.getValue(TreeValueExpression.java:114)
  	at org.camunda.bpm.engine.impl.delegate.ExpressionGetInvocation.invoke(ExpressionGetInvocation.java:40)
  	at org.camunda.bpm.engine.impl.delegate.DelegateInvocation.proceed(DelegateInvocation.java:58)
  	at org.camunda.bpm.engine.impl.delegate.DefaultDelegateInterceptor.handleInvocationInContext(DefaultDelegateInterceptor.java:92)
  	at org.camunda.bpm.engine.impl.delegate.DefaultDelegateInterceptor.handleInvocation(DefaultDelegateInterceptor.java:63)
  	at org.camunda.bpm.engine.impl.el.JuelExpression.getValue(JuelExpression.java:60)
  	... 54 more
  

Expected Behaviour
The start event with variable expression should get evaluated, and no exception should be thrown.

Hint

• The test works when using runtimeService.startProcessInstanceByKey().
• The startWithoutExecuting() method calls setVariables() after calling initializeTimerDeclarations() in contrast to the start() method.