Strange...
I thought anything you buy from Duty Free *is* allowed on board without even being looked at.
The restrictions about liquds hold only when you pass through security (X-ray, metal scanner, body patting, cavity search ... and more).
Once you clear this, you can pretty much buy any amount of liquids/alcohol and bring it on board.
Why these items would make less of terrorist tools compared to the ones purchaced elsewhere is logic that still evades me.
Sounds more like revenue protection than safety concern.