A serious payment glitch on retail website Overstock.com, which sells everything from furniture to diamond rings, allowed customers to pay with either bitcoin or bitcoin cash interchangeably. It’s a problem because the two cryptocurrencies, which split off from one another last August, have wildly different valuations.
According to CoinMarketCap, one bitcoin is currently worth $13,880, while a single unit of bitcoin cash is valued at $2,355, meaning those who paid with bitcoin cash could buy an item for a fraction of the asking price. Worse still, if a customer paid in bitcoin cash and wanted a refund, Overstock’s system would refund the customer in bitcoin, giving the user more money than they initially paid. It’s not clear how many customers may have taken advantage of this error.
Personally I don't expect many people were affected or exploited the glitch, other than the guy mentioned in the article, who apparently did this on purpose, just to see what happens.
Anyhow, Coinbase (Overstock's crypto payment processor) claim to have already resolved the issue.