Useless bike racks. Put your front wheel in the bracket, locl the wheel to the bracket. Some Low Life comes along and flips open the quick release skewer on your wheel and takes the rest of the bike leaving the front wheel locked to the bike stand. OK so Low Life had to buy a new front wheel, but the rest of the bike could easily be worth £1,000 or more.
There are workarounds, but much simpler to install a proper bike rack in the first place. Simple hoops, where you can thread the lock's chain round the cross bar and then through the wheels if you are really paranoid.