Why?

https://www.pivotaltracker.com/story/show/82974300 Didn't work for some user... and I guess we're so close to the wire, temporary removal seems more prudent than debugging.

Exactly. The serverside async processing does not work with Tomcat 7.0.52 out of the box installs, nor with default setups with certain Jetty versions.

• Jetty 7 was Servlet 2.5 (no async)
• Jetty 8 was Servlet 3.0 (async introduced) - spec was vague on what was default, so Jetty defaulted to async-supported == true
• Jetty 9 is Servlet 3.1 (even more async) - the spec was clarified, and jetty chose its default poorly. The default according to the spec is async-supported == false

Given the minimal benefit of async fixity checks and the certain confusion and email traffic debugging community issues, it does not seem worth it.