I don't have my laptop here (and won't be back to it until the new year), but the steps were this:
1 - select photo
2 - open Stationery Pad and have keywords entered ('info:neg={filename}, info:dev = XTOL 1:1')
3 - apply pad
at this point everything is ok
4 - open IPTC info and add a keyword. Anything seemed to work.
at this point colons were changed to pipes. I was checking with exiftool from the command line and Get Info in Finder. I think I could also replace steps 2 and 3 with the IPTC info dialog and manually enter a keyword, save it, reopen it, add another word, and save. It was after the second saving that colons changed to pipes.
I can't do any more tests until the new year, but I will gladly do them over and others when I get back.