gpg-agent: error accessing card: Conflicting use

[the2nd at otpme.org]

Hi,

i have a problem with gpg-agent when using it with a yubikey neo. after 
some time gpg-agent refuses to sign any data and so any ssh login with 
my key stored on the yubikey will fail. the gpg-agent log shows the 
following messages:

2015-05-30 13:49:36 gpg-agent[3600] error accessing card: Conflicting 
use
2015-05-30 13:49:36 gpg-agent[3600] smartcard signing failed: 
Conflicting use
2015-05-30 13:49:38 gpg-agent[3600] error getting default authentication 
keyID of card: Conflicting use

the command to start gpg-agent on KDE login is:
eval "$(/usr/bin/gpg-agent --daemon --enable-ssh-support --log-file 
~/.gnupg/gpg-agent.log)"

i haven't found the exact circumstances when it happens but its more 
likely to happen when the yubikey was plugged off and re-inserted, but 
it also happens without pull off from time to time. a restart of 
gpg-agent fixes the issue. it also often happens after i've pressed the 
yubikey button to generate an OTP but not always.

gnupg version is 2.0.27-r1 running on sabayon linux.

when using the same yubikey on my ubuntu 14.04 notebook at work i never 
had this problem.

thanks for any help.

regards
the2nd