I can confirm this is happening. This is due to the way chromium is architectured. This is caused because Blink dispatches the request to Browser which then dispatches the request to Network Stack. NetStack then sends the request out and then gets back the 408 and decides to retry the request without letting Browser or Blink know about it's retry attempts.

Devtools has our hooks in Blink and Browser but not NetStack. Fixing this would require a lot of effort.

I am not sure if or when this will be fixed, but I will leave it open.

Thanks!

I'm seeing a similar issue with GET requests that return a 204. I see the initial request in the Network tab of Devtools (and in our server logs), but if start filtering the Network I start receiving duplicate requests. Could this issue be related?

#5 Possible, but more probability of your issue being caused by: http://crbug.com/613188

It doesn't look like I have permission to access http://crbug.com/613188. 

#7 Sorry, I forgot to see if it was restricted. But I believe this issue is caused by the same thing in the linked issue. Sorry, but this issue was posted by an @google and linked some corp stuff so I cannot remove the flag to make it public.

I'll post here if/when there's an update.

Issue 613188 has been merged into this issue.

It looks like this is not something we can solve right now without a huge overhaul to many areas. The netstack is the area this is being resent. The request comes from one process (renderer) then it forwards to browser process. The netstack eventually gets it (and according to spec) a request gets recreated. We could send it back to the renderer to get an "ok", but that would only be useful to devtools and does not seem worth the effort.

Thanks for the report, but the good news is that it is surfaced in chrome://net-internals/