How to get Google OpenID auth working for migrated users (from SE)?

It issue has already been seen on OSQA meta, i.e. in Stack Exchange migration to same domain break Google OpenIDs.

I suppose I do have a very same problem with my migrated site. I started testing from Google OpenID logins and it appears that when I login with Google OpenID for existing user, the OSQA instance thinks that I'm totally new user.

I did some debugging and assoc_key that I'm getting whlie trying to login with OSQA is different that the one in (migrated) db - so clearly OSQA thinks that it's a new user.

I'll add that we stayed with a domain from before migration - so different domain is not the issue.

Furthermore I investigated what requests are sent to Google while trying to authenticate. Hence, OSQA sends:

https://www.google.com/accounts/o8/ud?
openid.assoc_handle=AOQobUd6RGCbjyqugHAKQ0LiHychGyLKfb1mZsXtjFUspo4AligkGSF6&
openid.ax.mode=fetch_request&
openid.ax.required=email&
openid.ax.type.email=http://axschema.org/contact/email&
openid.claimed_id=http://specs.openid.net/auth/2.0/identifier_select&
openid.identity=http://specs.openid.net/auth/2.0/identifier_select&
openid.mode=checkid_setup&
openid.ns=http://specs.openid.net/auth/2.0&
openid.ns.ax=http://openid.net/srv/ax/1.0&
openid.realm=http://mysite.com/&
openid.return_to=http://mysite.com/account/google/done/?janrain_nonce=2011-01-06T07%3A56%3A47ZYSTuEB

And SE sends:

https://www.google.com/accounts/o8/ud?
openid.mode=checkid_setup&
openid.identity=http://specs.openid.net/auth/2.0/identifier_select&
openid.ns=http://specs.openid.net/auth/2.0&
openid.claimed_id=http://specs.openid.net/auth/2.0/identifier_select&
openid.realm=http://mysite.com/users/authenticate/&
openid.return_to=http://mysite.com/users/authenticate/?token=AGh0dHA6Ly9zcGVjcy5vcGVuaWQubmV0L2F1dGgvMi4wL2lkZW50aWZpZXJfc2VsZWN0DQpodHRwOi8vc3BlY3Mub3BlbmlkLm5ldC9hdXRoLzIuMC9pZGVudGlmaWVyX3NlbGVjdA0KaHR0cHM6Ly93d3cuZ29vZ2xlLmNvbS9hY2NvdW50cy9vOC9pZA0KaHR0cHM6Ly93d3cuZ29vZ2xlLmNvbS9hY2NvdW50cy9vOC91ZA0KMi4wDQo%3d&
openid.ns.sreg=http://openid.net/extensions/sreg/1.1&
openid.sreg.required=&
openid.sreg.optional=nickname,email,fullname,dob,country

It's easy to see that these two are different. OSQA uses AX and SE uses SREG. return_to link is different.

How to get Google OpenID working?