According to [1], the previously accepted syntax was never documented as being valid. That means that code affected by this change was relying on undocumented behavior.
> As a shortcut for this.property, you can use @property.
It also said that since March 2010 according to the Internet Archive's Wayback Machine. Why did this fellow decide to use `property` instead? I don't know but I wouldn't hold this specific situation against the Coffeescript team. But that's just like my opinion, man.
A totally reasonable response would be "Oh, sorry, I had no idea people were using that in that manner."
Fine, fair enough.
But! It was known that people were relying on that behaviour and it was mentioned in the changelog. That is a big point in favour of Jeremy as a package maintainer. Not only does he know how his code should be used, but he has an understanding of how people are using it in the wild. That's wonderful and praiseworthy.
Where I get grumpy is that this was seen as a significant enough event to mention to the humans who happen to be reading the changelog. Yet, it wasn't deemed appropriate to tell all of the computers that are installing dependencies about it.
When you use undocumented behavior, is it correct to blame the project and take no blame for yourself? That seems to be what happened here.