Syncing deleted contacts with my phone

Just started today with AirDroid. It looks great!I deleted some contacts on my PC and synced again.
But the deleted contacts are coming back.
It is, I think, because AirDroid doesn't overwrite my phone contact list. Is it?

How can I activate this option to overwrite my phone contacts?

Phone: HTC One

@Elsy Does this happen all the time or just a rare case?
Would you please refresh and try again to see if it works?