upload-pack timing issue on windows?

As some of you might know, I've been working on porting git-daemon to
Windows for quite some time now. As it stands now, there's really only
one known issue that is blocking on my end here:

Something weird happens *sometimes* when upload-pack is exiting,
leading to a client dying with a "fatal: read error: Invalid
argument\nfatal: early EOF"-error. If I place a sleep(1) at some place
after exiting the while(1)-loop in create_pack() in upload-pack.c, the
symptom goes away. create_pack() contains some async-code, but this
doesn't seem to be triggered in my minimal case at all. I've tried
flushing stdout and stderr explicitly, no luck.

How often the issue triggers seems to depend on two things, the size
of the repo and the connection speed. If I clone from localhost, I
can't get it to trigger at all. If the repo is of some size, it
triggers rarely. However if I have a repo with only one commit, it
seems to trigger every single time for me.

I've noticed that one of the last things that happens is a call to
poll with nfds=1. This triggers a special case in our poll-emulation
on Windows; but removing that special case hasn't given me any
positive results.

Does anyone have a hunch about what might trigger this issue?

-- 
Erik "kusma" Faye-Lund