Why is there a doubled name in the Photos app when I search to name faces?

One is the original name tag you supplied in iPhoto, the other is the closest possible Contact in your Address Book.

I went through the same process yesterday - trying to decide whether I wanted people tagged as names, or Contacts.

I can find no way to switch it off - nor, even more irritatingly, how to assign all photos with a particular face to the Contact instead of the original name, other than one at a time…

Edit:
Simpler than I first thought - Select one 'Face' in the main faces screen, click the name & start to type. Choose whether to use the Original tag name or the new Contact name. All similarly-tagged faces will be changed to the new system & the old tag will vanish.

I made a silly one as an example…

• a. Start to type, you have 2 alternatives, select the Contact name

• b. Hit Enter, the Contact Name is embedded

• c. Try to repeat the process… there is now only one choice for that person [or cat]

There's a huge, detailed Photos guide on iMore - How to use Photos for OS X: The ultimate guide

It happens because iPhoto, when facial recognising was born, doesn't support contact integration so, when you recognise faces you link them to "handwrite" labels, not a contact.

Later, iPhoto was updated to support contact integration so, after this update, you can keep linking faces to handwrite labels or start linking them to contact labels. But iPhoto isn't able to merge handwrite whith contact labels and it generate confusion because, in lot of libraries, start born lot of faces with double labels.

To correct this issue you can merge manually all handwrite labels with contact labels. To do that:

• go into Photos faces screen.

• find faces which has two label for the same person (for example, in your faces screen, you have two labels for Bartłomiej Semańczyk probably strewn between all your faces; one with, as picture in the circle, his faces rotated 90° (which is the handwrite label) and one while he's swimming (which is the contact label) ).

• select one of the two labels for that face, I suggest the handwrite label (in your case the one with rotated picture), and click on the name label to rename it, start typing the name then, when appear the suggestion list, select the other label for that person (in your case the one while he's swimming).

Photos (or iPhoto, is the same) will merge that faces into the same person.