When I am creating a list of 2 or 3 destinations and 2 or 3 route numbers, then the button that lets me enter a 2nd route number doesn't put this next to the 2nd destination.
It is important to note that this dialog requires you to enter just one destination block at a time for one route. You need to pick the 'Draw' button at the end of the 1st destination/route block and then you can now enter the second destination and route into the dialog when it pops up a second time.
You do not enter the whole list in one go and pick an OK button. You are expected to enter each destination block, one at a time, picking 'draw', 'draw', 'draw' until you get to the end of the list and then pick 'finish'.
There is a button labelled 'Add 2nd, 3rd Route', but this is not for a 2nd/3rd destination in a list. This button is for the rarer situation where you have one destination but two route numbers associated with that destination.
For example - Birmingham A42 (M42) needs a second route number for the one destination as you would use this 2nd route button. But Tamworth A42 and Birmingham (M42) one has one route number for each destination so you wouldn't use the button, instead you would enter Tamworth A42 first, then press the draw button, then enter Birmingham (M42) next, then press 'draw' again.