Nick,
I ran a capture of ITTY:
...
10000 T
11011 FIGURES
01110 :
00100 SPACE
11111 LETTERS
01001 D
...
From the video I briefly saw, it seemed that the # was being printed after the colon as a separate impression. In the M28 typebox, space is right beside the # sign.
What I think I was seeing:
...
10000 T
11011 FIGURES
01110 :
00101 #
00100 SPACE
11111 LETTERS
01001 D
...
Maybe what's happening is that something is out of whack enough that the hammer is being operated just as the typebox is sliding into the blank spot reserved for spacing, so the hammer strikes the #, then slides off into the spacing position. It would be interesting to see the slow motion video of it if you can figure out how to upload it.
You mentioned that this doesn't happen with a period, but the period is in the same row as the space... Maybe try 0, 8, (, 1, 7 instead? Something to do with the distance traveled, maybe?
- Keelan