Historically we have had to ask the Captain for permission to use the handcuffs which has relevance given their stowage position.
Other restraint devices are NOW available to cabin crew without contacting the flight deck.
In many cases their the imperative to use them is so urgent that contact or permission isn't sought untill after the fact.
The issue of flight deck lockdown bears consideration
I can't imagine a situation at mainline where a Captain wouldn't be made fully aware of this type of scenario given that ultimately it is his/her aircraft.
Perhaps we are only getting half the story re the jetstar incident.
One would hope so.......