Well, I found a workaround solving this issue
$ sudo ifconfig eth1 down
The command down closes the network interface and up opens it again (more info here). After a reboot you have to close it again. Though, this could be considered a solution, it does not permanently solve the problem neither, does it provide a solid explanation WHY the interfaces are interfering and at what point. If anyone can provide an explanation I would mark it as solution.
EDIT: Typo