Halifax e-commerce fail of the day

I haven't had an e-commerce fail for a little while but the Halifax breaks the lull. It used to be so easy to transfer money between accounts. Your accounts all showed up and you selected which one to wanted to move money to. Couldn't be easier. Then they changed it so you had to enter the account details. Why do this? Is it to increase the risk of making a mistake and sending the money to someone else's account. Then there is no indication afterwards that the transaction has succeeded or might do in the future. You have no idea when or if the money will be available.

Then just when you resign yourself to the inconveniences, the whole thing falls over and you get this message.

Service Interruption
One or more of our systems are temporarily unavailable.

This means that you will not be able to proceed at this time.

We are aware of the problem, and hope to fix it soon, so please try again later. We apologise for any inconvenience.

So I can't do anything with my own money. Fail of the day is hereby awarded to the Halifax.
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The service did indeed return later but the transfer time turned out to be 48 hours. Is there a sensible explanation for why it takes two days to move money between a single user's accounts in the same bank?