nginx 1.11.0: client sent stream with data before settings were acknowledged while processing HTTP/2 connection

[locojohn]

Hello,

As of recently, shortly after updating nginx to version 1.11.0, we started
getting the following errors in the error log for our sites configured with
HTTP/2 and SSL:

2016/04/29 14:54:12 [info] 22321#22321: *290 client sent stream with data
before settings were acknowledged while processing HTTP/2 connection,
client: XXX.XXX.XXX.XXX, server: 0.0.0.0:443

This is so far only happening when browsing pages with Safari (9.1) and only
during a POST event.  Safari displays an empty white page with an error
message "Safari Can't Connect to the Server".  Our observations so far are
that this happens after some time of inactivity, which leads me to believe
that some kind of timeout has occurred (keepalive_timeout comes to mind).  
We have the following keepalive settings in nginx.conf:

http {
        keepalive_timeout 75s;
}

But this issue has never occurred before.

Any feedback/help is appreciated!

Andrew

Posted at Nginx Forum: https://forum.nginx.org/read.php?2,266525,266525#msg-266525