Sam Sutherland

While I totally agree that it should have been strict JSON from the start, the fact is that that wasn't the case.
I can think of three options:
1 (Hard to implement, solves most issues): Automatically edit all JSON stored in saves from earlier versions to put quotes around keys. This might break some JSON, but most command blocks should survive the disambiguation correctly. From 1.9 on, require strict JSON
2 (easy to implement, screws backward compatibility, still ensuring forward compatibility): Parse JSON strictly, everything else is invalid. This would annoy the hell out of loads of people, but would ensure forward compatibility.
3 (disaster): Keep the lenient JSON, while keeping as much backward compatibility as we'll ever get (definitely no better than updating all the command blocks) while breaking forward compatibility.

I'd go with option 1, option 2 breaks too much old stuff and option 3 is just silly.

In order to maintain backward compatibility, would it not be better to allow the more lenient json parsing, and just to encourage strict JSON adherence, maybe requiring it in new commands that are added to the game (or not, because that might get annoying - though it would encourage people to use strict JSON wherever they're adding new stuff) - I say that because I am currently working on a HUGE redstone project filled with command blocks, all of which use lenient JSON. It would take many hours to rectify this, and I'm not the only one who would be affected by this. Every creation using JSON from 1.8 backwards would stop working, causing even more custom map compatibility issues than 1.5

[1.7.2] I found that it occurred for me, about every 30 seconds, while I was building an underground staircase in creative, almost solid mining and placing. I have the latest graphics drivers etc.