Wrong dashboard showing

I recently updated from 3.05 to 3.12 with Buddypress 1.2.8

Everything works fine until, while logged out, I log in to the dashboard via a subsite (and not the main site).
Log in via https://www.mainsite.com/subsite1/wp-admin and not https://www.mainsite.com/wp-admin

Now all the links related to subsite1’s dashboard now point to mainsite’s dashboard.

This does not occur with subsite2 unless, while logged out, I log in to subsite2’s dashboard.

Examples of links now pointing to the mainsite dashboard:
In mainsite/wp-admin/network/sites.php – when the dashboard of subsite1 is clicked the page opens on mainsite/wp-admin and not mainsite/subsite1/wp-admin

When editing Posts/Pages in a subsite an error message “You attempted to edit an item that doesn’t exist. Perhaps it was deleted?” shows and the url is mainsite/wp-admin/post.php?post=2&action=edit and not mainsite/subsite1/wp-admin/post.php?post=2&action=edit