Dont’know if this is a bug or this feature has been removed. Same behaviour on sales order and sales invoice
Previously when you entered additional discount amount, percentage would get calculated automatically and vice versa.
Now only amount is calculated if you enter percentage. If you enter amount percentage is not calculated.
I am not sure if percentage was calculated earlier, but you can raise a github issue at Sign in to GitHub · GitHub for the same, we will take a look.
You are right. It wasn’t. Probably got confused with item discount, that does that. Anyway i think it would be nice if calculation would work both ways.I will raise an issue on github for feature request