The thing is that this is not actually going to happen. Programs are simply broken across the board, because few people can be bothered to deal with all these peculiarities.
The difference is, in Python 2, output would be corrupted in some edge cases, but generally it would "just work". In Python 3, the program falls flat on its face even in cases that would've ended up working fine in Python 2.
I don't think there's a general answer on which behavior causes less real-world problems total, but the idea that Python 3 makes less of a mess is not something I can agree with.