Can not login for Jids with a node containing XEP 106 characters

Openfire 3.9.3, authentication with xmpp-sasl, DIGEST-MD5. Steps to reproduce.

1. Create a user with a node having "@" character, e.g. pgstath@gmail.com@xmpp.test.im
2. Connect with PSI, or Sharp.Xmpp.
3. User is not authenticated

What both Sharp.Xmpp and PSI are sending during authentication, is of the form (decoded from base64):

username="pgstath\40gmail.com",realm="xmpp.test.im",nonce="X+qNuOnBmyqNsiZV6yMbG bW/xLA1SAmwrQptTcTz",cnonce="A6vgWDip/fqvLYDJvydXQInj+WNHUzZn/BmjhJFS7yM=",nc=00 000001,digest-uri="xmpp/xmpp.test.im",qop=auth,response=04da7eeeabe63546a270d3e1 50449784,charset=utf-8

This seems correct as far as XEP 106 is concerned.

User is authenticated with Spark but what Spark sends is this:

charset=utf-8,username="pgstath\\40gmail.com",realm="xmpp.test.im",nonce="HL9a4r mXyc3vAFYX3qOlWmCwgASEmVGZQuzDB8iW",nc=00000001,cnonce="Mat/uv8Ym3XwvE7HCccfDwH+ DMZwTOfiNQ81FTzJ",digest-uri="xmpp/xmpp.test.im",maxbuf=65536,response=402170101 fb2bb5f195d620407286214,qop=auth,authzid="pgstath\\40gmail.com"

I cannot keep from noticing  the pgstath\\40gmail.com part. My impression is that a double backslash is wrong and not conforming to XEP 106. Is this the issue why PSI cannot connect? Is this a smack bug?