If you are concerned, just pop into the EK office in Perth and pick up the voucher ( plus save time on arrival into DXB )

As long as your connection meets the criteria and you have booked it, there isn't anything to worry about

Looking at the schedules from PER-LIS in May, unless you are on EK421 which only has a 4 hour connection to LIS, then you are eligable for STPC ( subject to being in an eligable booking class )