plantuml : grouping sequence makes actor appears

Question

I am trying to make a plantuml diagram grouping some activation with notes on groups. It looks like this :

actor User as U
box SBCP
participant "First" as F
participant "Second" as S

U -> F  : "start"

group firstgroup
    note over firstgroup
        a first  note
    end note
    F -> S ++ : first 
    S -> F  -- : end first 
end group

group secondgroup
    note over secondgroup
        a second note
    end note
    F -> S ++ : second 
    S -> F  -- : end second 
end group

It works great except it generates strange pseudo actors :

Is it possible to remove this lifeline ?

to get something like (edited with paint.net) :

Thanks ,

Olivier

Answer 1

After asking plantuml forum the right workaround is to add the note on participand not group :

@startuml
actor User as U
box SBCP
participant "First" as F
participant "Second" as S

U -> F  : "start"

group firstgroup 
    F -> S ++ : first 
    S -> F  -- : end first 
' add the note to the right
note right: a note 
end group

group secondgroup
    F -> S ++ : second 
' add the note to the right
note right: another note
    S -> F  -- : end second 

end group
@enduml

the final result is