TYPO3 Core

Hello,

I am having the problem with my Browser (tested Google Chrome, Version 27.0.1453.116 m) that when I want to login into two different backends of TYPO3 6.1 instances it wont let me login to the second instance.
When I try to enter my credentials (they fit, I have them in my keepass file and they work if i use them in another browser) I will just get redirected to the login page again. The cookies are set however. If I hit F5 i have to relogin, which will not work, just like the first time.

My other customers have different TYPO3 version running (4.5 and 4.3) and there wasnt any problem when I try to login to both BE with the same browser (different window).

If I however see the BE for a short moment it will kick me out again without a message. Sadly the other instance will bug out and say the session expired. If I enter my password it will disappear and I can work, for roughtly 10 seconds until the window pops up again. When I logout and relog to the instance it will not work. I have to clear browser cache and cookies - then it will work again - for one instance of course.

Now I have 2 local TYPO3 instances running, both 6.1 and it wont work. (XAMPP).

Could this be some kind of bug?
Tell me what info you need, I will reply as fast as possible.

~pascal.