You will often find pieces that are identical in shape.

And perhaps if you are really really lucky...they have similar colours as well. Do not worry, it happens more often than you think, and it's common with every manufacturer I believe.

It can be annoying, I know.

It happened that when I was close to the conclusion of a puzzle (or even after completing it) I had to switch a couple of identical pieces because I noticed that the colours were slightly different or the pattern didn't completely match the surrounding pieces. That's life. Be patient (if you can).