Unable to change system variable path in Windows 10 as an Admin

Question

I am installing Java JDK in Windows 10 machine that requires registering its path by editing System Variables in Windows settings, but I tried both as an admin and regular user and it doesn't allow me to add the path, even copy paste or just adding any character.I have no trouble doing this in Win 8 until I am 'tempted' to avail and run free upgrade by Microsoft.

Q1:

Is this A bug in Windows 10? I update my machine regularly and also auto update is turned on to ensure to get the latest fix from Microsoft. Kaspersky is also disabled temporarily.

Q2:

How do you edit the system variable in Win 10 machine? I am planning to downgrade my Machine to windows 7 or 8 if this issue is not fixed.

Any ideas?