Is this a dangerous multifeed?
The evidence would suggest that it is an improperly wired multi-wire branch circuit. The two legs of the circuit are erroneously and dangerously shorted together somewhere. When a MWBC is properly wired, the only path from one leg to the other is through the loads.
The reason the two breakers are on the same pole is some delirious spark monkey discovered that if installed properly they trip instantly when main power is restored. He was unable to discover the real problem but by moving stuff around at random he effected a miracle cure.
The quickest test for a real short circuit, as opposed to a phantom voltage transmitted through the loads, is to properly position the breakers on opposite poles and see if they trip immediately.