I don't know whether this is network-wide or just on SO, but chat doesn't onebox meta.se comments when I've come to the post through the Meta newsletter and so ?newsletter=1&nlcode=x
is in the URL
It should!
i.e.
http://meta.stackexchange.com/questions/236552/ignore-american-and-british-
english-spelling-differences?newsletter=1&nlcode=83%7ca920#comment775901_236552
vs
http://meta.stackexchange.com/questions/236552/ignore-american-and-british-
english-spelling-differences#comment775901_236552
It took us a while in the Lounge to figure this one out, which therefore must be deemed to violate the principle of least surprise.