Login for Google Profiles account doesn't work after joining Google+

After joining Google+, the profiles.google.com/username URL redirects to plus.google.com/[long number]/posts. When trying to log in on SO using the profiles.google.com URL, I got (line breaks for clarity):

Unable to log in with your OpenID provider:

The OpenID Provider issued an assertion for an Identifier 

whose discovery information did not match.

Assertion endpoint info: 
ClaimedIdentifier: https://profiles.google.com/username 
ProviderLocalIdentifier: https://profiles.google.com/username 
ProviderEndpoint: https://www.google.com/accounts/o8/ud?sourc

e=profiles 
OpenID version: 2.0 
Service Type URIs: 
Discovered endpoint info: 
[{ 
ClaimedIdentifier: https://plus.google.com/longnumber 
ProviderLocalIdentifier: https://plus.google.com/longnumber 
ProviderEndpoint: https://www.google.com/accounts/o8/ud?sourc

e=profiles 
OpenID version: 2.0 
Service Type URIs: 
  http://specs.openid.net/auth/2.0/signon 
  http://openid.net/srv/ax/1.0 
  http://specs.openid.net/extensions/ui/1.0/mode/popup
  http://specs.openid.net/extensions/ui/1.0/icon 
  http://specs.openid.net/extensions/pape/1.0 
},]