Zendesk defaults so that when you apply an update on a ticket and click 'submit', it closes the ticket and returns you to your previous page/dashboard.
This isn't ideal if you (like me!) prefer to apply multiple updates on the one ticket.
A handy tip to enable you to do this is to select "Stay on Ticket" from the grey box next to "Submit as ***'.
Just in case you missed it (like I did until today), the option is located here: