Problem with gpg-agent and yubikey since openssh v6.8p1

[the2nd at otpme.org]

Hi,

i'm unsure if the problem we encounter is a bug in openssh or in gnupg. 
But as everything was working with openssh 6.7p1 and earlier i guess 
that there where at least some changes in openssh that leads to the 
problem.

You can read the latest discussion about the problem here:

https://www.mail-archive.com/gnupg-users%40gnupg.org/msg29421.html
https://www.mail-archive.com/gnupg-users@gnupg.org/msg28416.html

I hope to get some help on this list as its an very annoying problem and 
using an old openssh version is just a bad workaround.

If you need any more information or help debugging i'm glad to help.

regards
the2nd