Who shows when someone calls all-in on the end?

[Siegmund]

The hand that provoked the incident actually occurred online, but since the B&M forum is the one which is frequented by real-life floormen.

I am in a limit $2/4 game, shortstacked. I have AA, and by the turn, it's just me and one other guy, and I have $10 left.

He bets, I raise, he calls. I have $2 left.

On the river, he bets $4, I call $2 all-in, he takes his other $2 back...

and now *my* cards are faced, and *his* are mucked without being shown.

I inquired of support as to whether this was a bug, and received a polite reply: "Thank you for your email. I have had a look at the hand in question and would like to state that the other player has the option of mucking his cards as he was not all in."

Is this normal? First time I've seen it. I guess it only comes up if someone calls all-in on the river specifically, since otherwise both hands would already be face up.