Every other ticketing system I've used, either at my current position or previous positions has had the ability to upgrade incident tickets to problem tickets.
When upgrading, it should put the incident into a closed state and auto create a problem ticket with all the incident's comments and notes.
Would be good to also have the option to select multiple incidents via the normal tick boxes, and upgrade them all to a single problem ticket.
When this occurs, it should ask for the problem ticket's main text and title and then auto relate all select incidents to this problem and set them as closed.