Neutral auction houses

Today I tried to give 4 decent bags to my latest Ally alt in Booty Bay. I however wasn't able to buy or even bid the bags I put on auction with my Horde main: I kept receiving the message "you can'y bid on your own auctions".
However, I gave money to the very same alt in the very same way months ago: I sold a pumpkin for 1,000g in the neutral AH in Booty Bay and I bought it with my Horde main. Now, by doing the other way around (putting on auction cheap containers for my Ally alt to buy) I received that puzzling message.
What happened? Did they change how neutral auction houses work?

You used two accounts before, now you're trying it with one.

You can't buy auctions you posted from the same account.