In their presidential elections at least it's pretty much by design. It happens because they have 2 rounds.

The first round the far-right option gets a relatively large amount of votes. Then the round after only 2 options remain, so anyone who doesn't want the far-right option just votes for the only other option. Not sure what happens in general elections, but presumably it's somewhat similar because there's still 2 rounds.

As far as election systems go it has quite a lot of obvious flaws, but it's perhaps not quite as bad as first past the post. At least it makes the tactical voting a bit more straightforward.