Why won't haproxy capture my cookie?

I'm having trouble getting frontend cookie capture to work in haproxy. I have this in my config:

frontend frontend 0.0.0.0:9999
[snip]
capture cookie foo len 10

Then I use nc to talk directly to the server and send it:

GET / HTTP/1.1
Cookie: foo=bar

I get a log line, but there's a "-" where the captured cookie should be.

From stackoverflow

• You're using version 1.3.15.2, but there's a cookie capture bug that wasn't fixed until 1.3.15.6.

  mike : Thanks, that's exactly what it was!

  skaffman : I appreciate that sometimes talking to yourself is the only way to get an intelligent conversation, but this does look a bit odd.