With your multi-user feature, is there any plan to introduce any sort of record lock that stops two users from amending the same invoice at once?
Currently, two different users can access the same invoice, edit and make changes, and it is the user who saves their changes last who will have their changes saved. The user who saves first will have their changes lost, even though it looks to them like everything has been saved correctly.
While the chance of two people being in the same invoice at once is not high, it is a still a vulnerability and over a long enough time it is going to result in an error.
That's pretty shocking that you have no intention of implementing this. It's well known best practice and taught to programming students. I don't know why I'm surprised though.