HAProxy Page Element Request Times Slowly Increase (no replies)

Hello All,

I've got a strange issue with our deployment of HAProxy 1.6 where a user
will make a request to a page, and as each page element comes in, the time
taken shown on each file downloaded in the IE developer tools increases by
a factor of 3, until finally the user is prompted for credentials, but the
page load never continues. I should mention that this is an ASP.NET web
application running with Integrated Windows Authentication on IIS 8. I
know, I know, IE + IIS + IWA = terrible, but it's hard for the enterprise
to not use these platforms internally, especially the IWA single sign on
part.

So a request looks like this in the developer tools:

mainpage.aspx - HTTP 200 - 130.04KB - 421ms
css file - HTTP 200 - 1.51KB - 296ms
css file - HTTP 200 - 14.93KB - 0.96s
css file - HTTP 200 - 13.99KB - 2.73s
css file - HTTP 200 - 29.92KB - 8.14s
css file - HTTP 200 - 23.44KB - 24.36s
webresource.axd - Pending - Pending - Pending (this is where the user is
prompted for credentials)

And on that last file is where it then prompts for credentials, which never
works because I believe that HAProxy has hit the timeout and closed the
connection, and breaking IWA.

I should mention that our HAProxy server works great 99.9% of the time, and
we do a lot of L7 load balancing on different URLs, and host headers, and
we handle a good amount of traffic that returns page elements in ms, and it
also handles Integrated Windows Auth fine - most of the time. It's just
these occasional things that have me at a loss.

Any suggestions from the mailing list?