This thing actually happens ALL THE TIME in Bitcoin. That's why no one accepts a transaction (at least not one for any significant amount of BTC) as soon as it

This thing actually happens ALL THE TIME in Bitcoin. That's why no one accepts a transaction (at least not one for any significant amount of BTC) as soon as it is in the latest block - they wait until the transaction is in the 3rd, 4th or older block. The Bitcoin blockchain constantly "forks" for the latest 1-2 blocks. If you sell your car for BTC and hand over the car the moment you see the latest block contains the transaction where the BTC enters your wallet, you may see 1h later that the longest chain does NOT contain your transaction, and in fact your transaction is now invalid, because the buyer wallet has sent all the money somewhere else.