[squid-users] authenticateDecodeAuth error

[oleg-s]

hello.
recently switched to auth scheme "Digest" with squid 2.5.STABLE3.
and found this in my cache.log :
-----------------------
WARNING: failed to unpack meta data
authenticateDecodeAuth: Unsupported or unconfigured proxy-auth scheme, 'Basic 
<base64_encoded_string>'
----------------------
is this a misconfigured|buggy|broken client software or should i do something with 
squid.conf?
all clients work w/o problems, but this message is printed to log periodically.
thanks for answers.
olegs