There's also the question of exchange rate changes between the date of purchase and the date of refund. You take this risk. I'm awfully sure I've seen a warning about this in Citibank's terms and conditions. Anyway, no matter the bank, I always know I'm going to lose a bit when refunding a foreign currency charge. Not sure I've ever gotten precisely the same back as I was charged.
As to Citibank (HK) and foreign transactions generally, I just had an AirAsia purchase in HKD rejected by Citibank. When I called, they said their system rejected it because the billing was in HKD. If AirAsia had billed in another currency, no problem.
I know some banks in HK charge a foreign transaction fee on HKD charges if the charge arises outside Hong Kong. But this is the first time I've encountered a complete block. Not happy with Citibank! And I find no warning in their terms and conditions that they do this.