Just did the border run from Hua Hin to Padang Besar with a return on a sleeper train, same day! Do not try it! You now have to spend a night in Malaysia before returning. Tried to buy a new return ticket. All trains full for 6 days. Ended up with minivan to Hat Yai and 11 hours by bus to Hua Hin. Next time I'll go to Myanmar or Cambodia.