I seem to remember there being a similar issue with this in Toad 9.5 but I think that was when the auto replace contained a full stop. So if your auto replace was .con you would be able to type msi.con and it would expand to msi.concatenated_segments. The answer then was that the full stop was a special character and could no longer be used in that way so the workaround was to change the auto replaces to remove the full stops and the end result would be the same.
I expect the reason for it not working now is because it is treating the entire string msi.con as one entity rather than the 3 that it used to. Apparently this is for lexing purposes - I raised it in a previous post on this forum regarding auto replace where I mentioned that while ROWID is highlighted if I don’t use a table alias, as soon as I do (i.e. a.ROWID) the highlighting is gone. As it was just a highlighting issue, I didn’t think it was much of a problem but maybe it is causing other problems too and is worth revisiting?