Two things:
First, the contacts will merge any contacts that it identifies as the same into a single contact. So when you create that second version of your husband with just his first name, as soon as you hit "done" it merges that with the already existing one because it matches the first name and mobile phone number. This is convenient when you have several accounts with duplicate contacts as it will not display multiple versions of the same contact. In your case it is a small nuisance. You can however go to the contact, then menu, then separate. This will give you 2 separate contacts.
Second, you are going to more trouble than really necessary if you are simply trying to make a speed dial shortcut for your husband's cell. You can simply go to your home screen, menu, add, shortuct, direct dial, then find his cell in the contact list. It will list each phone number separately so you can choose which number for each contact you want to use for direct dial shortcuts. This method will not allow you to change his name to display first name only however.
Hope that helped,
Troy