I don't think it's a problem. I'm trying to find you a picture, but for now...
Inside the shrink wrap is a canister which is the cell, the button is placed on the positive end of the cell and a plastic washer is put over the top of the button to keep it insulated from the canister. Then the whole thing is shrink wrapped.
In your case, I think the plastic washer wasn't pressed down enough before the wrapping. If it works don't fret. If it bothers you, send it back or buy some shrink wrap tube (always good for repairing torn wrappers anyway) and rewrap it. You can find it on Amazon under 18650 shrink wrap, I think.
Here's a pic....
The picture is a link to the original thread, have a look, you'll never want to use an Untrafire cell - ever.
It looks fine to me and if it were mine I would go ahead and use it. The only issue I could see possible is that it may not sit properly in some manufacturers reverse polarity protection designs...like that of Eagtac. That's only a maybe though and would just be caused by the wrapper and washer not allowing the electrode to contact the cell button because it's in the way.