- there is a three-level execution hierarchy: Process Instance <--- Scope Execution <--- Concurrent Execution
- the element variable is set on the concurrent executions, but BusinessProcess#getVariable accesses the scope execution for the first MI instance. Thus, the variable cannot be resolved
- BusinessProcess#getVariable relies on the current execution context, i.e. Context.getExecutionContext()
- the execution context is updated whenever atomic operations are executed
- the first MI instance is not part of an atomic operation (cf ParallelMultiInstanceActivityBehavior and MultiInstanceActivityBehavior#executeOriginalBehavior ll 197-201), thus the first concurrent execution is not pushed onto the execution stack
1. Quick: push the first concurrent execution onto the execution context from within MultiInstanceActivityBehavior#executeOriginalBehavior. Ensure that the context is removed again under all circumstances.
2. Implement MI as a proper concept in the PVM.