All of our handsets are Snom 360s. Switch is 2xi

To dial another extension (or to make an external call) you can just key in '2' & '7' and wait 3 or 4 seconds and it will ring the target extension. Alternatively '27#' places the call with no delay. Similar with external calls.

My new Snom 360 requires the user to enter '27' and to then press the tick button. Without pressing the tick nothing happens however long you wait. Same firmware as other phones.

What controls this behaviour? I just cannot find any difference in the Snom or Quadro settings between extensions with these behaviour differences.