Nope! Haven't seen this. You should save the replay. I don't play 3DS
I just made a replay but the glitch does not show on replays. I could not reproduce it offline either, only online.
It is pretty easy to reproduce though. I just did it on purpose and to do that I just went to FG 1v1 and when my opponent was losing his last stock I flew out of the screen using Robo Burner so that I was offscreen when the announcer said "game". Then I just dropped down without deactivating Robo Burner mode and saw the flames coming from above the screen but R.O.B. was invisible. When watching the replay I did see his base though, but I am sure he was invisible in the actual match, especially since I have been seeing this glitch multiple times and the first time that I saw it was probably months ago.
So you need to be offscreen when the announcer says "game" and then you need to get onscreen again before the transition to the victory screen when playing online.
In addition to that some things that may or may not be a requirement are using Robo Burner, using R.O.B., being on FG 1v1, and doing it on the 3DS.
I am pretty disappointed now I know that this does not show on replays though, partly because it would be a much more fun way to end the game if it did and partly because now it might seem like I am lying and this might seem like a lame excuse =(
