Logging into two seperate facebook ids affects User Map

Hi,
Whilst trying to test scenarios which may cause my looping problem, I have come up against an interesting scenario, which affects the User map and subsequent logins

I opened multiple browsers in the same product - ie Firefox.

I logged in with Facebook to the first session, logged out, didnt close all browers went to the next session (cant remember if it was a new tab or window), logged into facebook as a different facebook id.

Instead of there being two seperate entries in the User Map for each user, what i find is that there is one entry in the User Map, but the picture is from the other user.

When you then log into the site with the first id again, the user is logged in, but the picture is the wrong one.

If you login in FB, close all browsers and then login again with the other user, it works correctly and adds the User Map properly and subsequent logins show the correct profile pictures.

This is a weird scenario, but can be a problem scenario

Rich