4) Someone looking at this tx list will spot some of the failed transactions and modify them so they become bitcoin-0.8+ compliant. This gives a new tx and the transactions get through. MtGox fails to spot its own tx in the blockchain; gives up and returns funds to the customer.
do you have proof that the balance has been refunded?
This is standard procedure by MtGox. If a transaction gets stuck and doesn't get processed MtGox will refund you. Has happened to me 2 times personally.