Take a look at this http://www.treccani.it/vocabolario/difetto/
The only use of "per difetto" that existed before a translation of "by default" was ever needed is in the expression "approssimazione per difetto", and the new meaning forcefully attached to "per difetto" makes sense only in the worst nightmares after a "peperonata co' e cozze".
Picchi probably is only witness of a niche neologism, that was probably bred from a bad technical translation. But it was a bad neologism in the first place, it was incorrect right from the start.
EDIT Nevertheless I take your point: you did your research before you wrote "correctly".