I don't know much about electrical regulations outside of NA so for all I know that might be normal, but it looks very dangerous to me.  My guess would be TP Link is only using a single relay to pass the live (line) current, and if so I suspect that the other line, passed straight through, is carrying current/voltage as well or instead.  In NA only the live line has voltage, the other is neutral and safe to touch when the power is off (though you should never!) and typically you can't plug it in the wrong way as the tangs are different sizes.

I'd suggest further research into wiring regulations there, but one thing to try first would be to turn the HS110 around 180 degrees to see if that helps (assuming you can do so).  Since you're using an extension perhaps it's possible you've got it plugged in upside down.  I'd also confirm that the home wiring has been done correctly, and ideally was properly inspected.  It's possible (but probably unlikely) that the TP Link engineers designed the wiring backwards.  Good luck!