We have a series of recurring issues regarding specific line items. I even created "similar but new" line items so that we wouldn't get the conflict, but it is still happening:
When using item # DTC CC-FLAT-FEE-CONTRACT or DTC CC-MATERIALS we have to open up the invoice - and re-enter the information using the same number once it is in the invoice. We originally add those line items from within the service ticket area.
I tried removing the old numbers, and putting in new, undeleting original, nothing seems to fix the issue. Once we have redone the lines from within the actual invoice it works fine -- and since it is the exact same line item # that we put in from the service ticket, I'm at a loss.