The problem as I see it is that the net needs to be specified at the beginning
of each line to indicate which net the following nodes belong in. Until a new
or different net is specified. The same principle is true and used in the setup
of many pieces of FTN software.
I would surmise that the Seen-By lines are not looked at as one continuous line
but as separate sequential lines. And therefor the net specification would need
to be specified at the beginning of each line.