funny - these words are all from /usr/share/dict/words from my ArchLinux system, blame them :)

repeated - yep, this surprised me.
There are several ways this can happen. Take 'food', put a 't' over the 'd' and get 'foot', next put a 'd' over the 't' and get 'food' again.
Or put an opposite transpose word over some letter and then replace that letter in a subsequent move.
I've seen 3 or 4 copies of the same word in some runs. I think I'm following the rules of Upwords, but I've never played the real game.