First of all this is very hard to describe and for me to debug, so the best I can do is say what I'm running it on, and what I've tracked it to thus far.
I've seen this since 3.0 because that was the version of WordPress I started with in my current platform setup.
Cherokee Web Server 1.2.1
I'm running WordPress behind a firewall, and reverse proxied to my dev domain.
I am also running MULTISITE with subdomains.
Where I see the problem is when trying to update WordPress automatically, or to be more specific when trying to update the database from the tools > update page.
Like I said before, I've tracked it down to the wp_remote_post function, which is called to run the update database script from the admin.
I have taken the same URL, which is:
Then I try to call that URL directly through a web browser and it works, then I try to call it directly from commandline curl and it works.
What happens when I try to run the update script normally from the admin is a timeout, and eventually a 500 error. Then the server seems to kind of 'lockup' for a minute or two, then it starts working again.
This has been very frustrating and I can't seem to figure it out. Any help would be greatly appreciated.