Did you have the 'controls' of the card set correctly? Mine had magstripe payments off by default. You have to choose to have that enabled. Same with things like location based protection, gambling payments, ATM withdrawals and online payments.
So long as that's on you should be fine, I've used Starling across the US and it's always been fine except frustratingly petrol stations but I can live with that.
edit - I've just checked, it automatically locks magstripe payments after a while and you have to enable it.