Various functionality in Yate changes by the presense of a multi-value delimiter in a field. For reasons of brevity we'll be using the default value of ;;; when referring to the multi-value delimiter. The major areas affected when ;;; is in a field are:
When fields associated with application lists contain a multi value delimiter (;;;) sequence, a popup list is automatically switched to append mode. You can remove the necessity of manually adding a multi value delimiter (;;;) sequence by holding down the Option key when clicking on the disclosure button to the right of the field. If you want to always append, configure the Always Append mode in Settings - Lists or on a field's function button.
Note that when the popup menu is visible and is in append mode, the field's text is displayed green and the type of menu displayed differs. If you are editing the field and type a down arrow key to activate the menu, Option will have the same effect.