Redmine

When I'm using two different Redmine systems (for example a working system and a testing system) within the same browser (tested with Chrome an IE), the autologin cookie registers everytime automatically the two users of each system with the same ID on the databases.

An example: I'm logged in on the working system with my work account. Now I open a new tab, go to the testing system and register myself with a test account.
When I'm now going back to the working system and refresh the side, I'm no longer logged in with my work account, but with the account of another workmate, which got the same ID on the working system database as the test account on the testing system database.

There is no authentification (password) needed, which effects that I am able to login with each user of the working system, as long as I got a user on my testing system with the same ID.