Hi Chris,
Based on your test and my test in 15.4 SU2, it seems that there was a fix implemented in this area that is not part of HF27. Therefore, if you need this working in v14 HF27, best course of action is to log a ticket with the Alliance support team to see if this can be resolved. Or upgrade to v15.4 (preferred long term anyway)
In any case, it looks like a code issue and not a data issue so will require a code change.
The only work-around I can see is to remove the link to the checklist via SQL from the invoiced order but then you don’t have the results of that checklist and this is not a recommended process to modify orders directly outside the application, especially those already invoiced which for all intents are basically read-only at this point.