Variation in switch manufacture, most likely. I have similar with one of my Duckys (whereas the other one is fine).
If it really bothers you, see if you can return the keyboard, although as all keys work (and click, if you press then right) the vendor might hesitate.
Or, if it is out of warranty, one possibility is to replace the switches yourself (but will probably require desoldering the old switches and soldering new ones in).