"Pin rejected" trying to disarm when alarm is going off

This afternoon I accidentally set off my alarm while it was in Stay mode (opened the back door before disarming). While the alarm was going off, I tried using my PIN on the keypad to turn off the alarm but it didn't work. I ended up disarming via the app (and then answered the phone call to confirm the cancellation). In the app, under History, I see "Pin rejected." I'm *pretty* sure I used the correct pin. Is it not possible to disable the alarm via pin when it is going off? Or is it more likely was I just rattled by the loud siren and fat-fingered the code?