Don't Steal from my Basket

Imagine this, it is sale season and you are at a popular fashion retail shop. You pick up a basket and you start finding bargains and putting them in. Then a few minutes before you go to the till, someone comes and takes something from your basket. How would you feel?
A couple of weeks ago, Elena (our creative head) experienced this online. She was shopping from the online shop of one of the mainstream fashion brands. She had added some items to the basket and continued browsing. When she was done she decided to check out. To her surprise, some items had disappeared from her basket and where not available in the shop any more. Apparently this online shop allocates the items to whoever checks out first and not who put it in the basket first. This is completely opposite to how we are used to shop.
It would make sense to have some timer of validity of the items in the basket, but in this case there wasn't. The system was basically removing items from the baskets if a new user purchased that item. The experience was ruined. The user was left frustrated and will probably think twice before shopping online from them. After all who could guarrante that their entire basket will not disappear next time.
When designing online experiences it is crucial to keep in mind what people are used to and what the real world experience is. Taking items from a person's basket is unacceptable in a shop so why allow it online?