I wondered this as well. Auto-replies are supposed to have a null sender, so the iPads must have been either ignoring the presence of the other's null sender or giving their sender a non-null value.
"Both wish to stop Iceland's entry to the European Union, which could excite the Pirate Party's support given its policies emphasise personal liberty."
I've been trying for years to get BT to explain why they won't show international numbers on caller display. I've never been able to get a straight answer.