This behavior isn't a bug. It's expected and necessary. It only changed if you are 1) POSTing in Javascript, and 2) not using Rails' built-in AJAX or unobtrusive Javascript helpers, which handle these details for you.
On top of that, most sites that use AJAX heavily and have this bug have it happen frequently enough that they investigate and fix it. In this case, the author's Javascript ran infrequently and unpredictably enough to make it difficult to trace (interestingly, having dealt with this issue before, I guessed the cause by the third paragraph).
It's the same principle behind the ThinkGeek Annoy-a-Tron. A loud, constant noise will drive you to look for it within seconds, and you'll probably be able to find it. But a brief chirp that happens semirandomly every fifteen minutes is incredibly hard to track down.
On top of that, most sites that use AJAX heavily and have this bug have it happen frequently enough that they investigate and fix it. In this case, the author's Javascript ran infrequently and unpredictably enough to make it difficult to trace (interestingly, having dealt with this issue before, I guessed the cause by the third paragraph).
It's the same principle behind the ThinkGeek Annoy-a-Tron. A loud, constant noise will drive you to look for it within seconds, and you'll probably be able to find it. But a brief chirp that happens semirandomly every fifteen minutes is incredibly hard to track down.