If one opens the trigger configuration, enable the trigger expression constructor, a new button "Insert expression" becomes visible.

If we hit the 'Trigger status "OK"' button it will actually insert:

{TRIGGER.VALUE}=0

If we hit the 'Trigger status "Problem"' button it will actually insert:

{TRIGGER.VALUE}=1

Both are not really needed anymore, and leftovers from Zabbix 3.0 when there was no "recovery expression" supported.

I think it's time to clean up this button and prevent some confusion.