"Activate/Deactivate already done" error in sequence diagram

Question

@startuml
a-> b: test
activate a

deactivate a
activate a
@enduml

This sequence diagram code causes an "Activate/Deactivate already done" error.
Tested in VS Code with beta .jar (http://beta.plantuml.net/plantuml.jar)
and online at www.plantuml.com/plantuml, result: 

Answer 1

You can add an hidden message (a-[hidden]->a)

See on PlantUML Server