Earlier quoted context omitted.
I was on the side of the person giving the - I think fairly legit., bug until I came to, "tax software in php" and then I realized there's nothing really black and white in this world.
Did you catch the part about "it makes you lose faith in the product"? ROFL
I think the PHP team changing the return value of a function without putting anything in a changelog is a Very Bad Idea and a dev. should be pretty upset about that. Saying that the main dev. is doing this work as a charitable thing is fairly misleading as well.
Buuuuut, I also think passing an unitialized value like that is already a bug in this context given the type of software being created. I'd rather see, "NULL" found wherever than know that it was magically changed to 0 (like they would prefer). I know the dev. said that this is just a formatting thing, but I'll wager they're using formatted numbers for some sort of calculation (inadvertently or not).
Whatever is going on, I hope there was a huge code review and a massive QA effort ( which I also doubt happened), because this is a textbook example of tech debt and the loan shark has come a-knockin'.