thx for all your work.
i might have found two bugs.
1: articles will be duplicated if you can save a bill (might also be the case for offers)
what i did:
create a bill, two rows / articles - the first has all required data / fields fill out.
the 2nd was missing the name / first field.
i hit save -> error message
but it will still be save, + for every time you hit save the articles which have all the required data will be dublicated (additional line) for every time you try to save.
2: if you use the discount field at the end of the bill, it reducses the total amount (what should happen) but the tax amount which is shown still remains the same. i.e. you have 100€, 20% Tax -> 120€ total, and add 50% discount the billing amount will be 60€ but on the tax field above there is still 20€ tax instead of the 10€.
i hope you get what i meant, and iam not sure if 2. is really a bug since invoice requirements differ from country to country.