Adding a new contact in iOS 8 merges it with a homonymous old contact I have in my iPhone iOS 8 and old contact called Salvador. This old contact has his mobile, and some notes, and that is fine.

Today I select a phone number from my call history and select the add a new contact option. I enter the name contact as Salvador and add a note to this new contact.

The problem is when I recall from my contact app the Salvador name, it only appears once (I'm supposed to have an Old Salvador and the new Salvador as a contact) when I select the Salvador contact the info inside is a combination of the phone and notes of the old Salvador and the phone and notes of the new Salvador.

Why is this happening?
You cannot have more than one contact with the same name in your iPhone so it sounds like your iPhone is merging them together. Try adding a last name/nick name to have them as two separate contacts.