Keep in mind I'm trying to test a TX/RX echo sketch, so I was loading the same sketch to both Arduinos.
Could it be due to using the same board and sketch for both instances? Unfortunately I tried something else (see below) and it didn't work as well.
I tried changing sketches for instance #1 in various places through the step I listed above. It did not make a difference. When I change the com port on the 'this' instance the instance on 'other' instance closes. Doesn't matter if I change port for board #1, then #2 closes or the reverse.
That seems to leave only having the same board (or something else that I don't know of yet). I will have to dig out the MEGA and give that a try.