When trying to enter a vehicle as passenger and the event has been cancelled for it before, the event is not triggered anymore and you are unable to enter the vehicle as passenger even if the event doesn't get cancelled the next time. This happens only when trying to enter a vehicle as passenger, entering driving seat does trigger the event everytime and trying to enter another vehicle as passenger works just fine. 
My code is as follows: 
 
function onVehicleStartEnter(enteringPlayer, seat, jacked) 
    outputChatBox("trying to enter vehicle...") -- for debugging 
     
    if (getElementData(source, "locked") and getElementData(source, "locker") ~= enteringPlayer) then 
        outputChatBox(" but it's locked") -- for debugging 
         
        cancelEvent() 
    end 
end 
addEventHandler("onVehicleStartEnter", getRootElement(), onVehicleStartEnter) 
 
Have I done something wrong, or is something broken in MTA? 
Thanks. 
Excuse me for my bad english, I hope you understand what I mean anyway.