ok here's the situation.
arc-fault holds until i turn on the light switch. or turn on a lamp, basically it holds till any load is put on it (other than small alarm clock).
it is wired correctly.
Old knob and tube rewire.
it is in a the new service panel which is being fed by a jumper until the PoCo hooks up the new service. it is only feed by 3 wire (2phase and neut.) but there's Gr. Rods on both ends.
it's a Square-D arcfault, which they were having problems with earlier, these are supposed to be new ones. happens to all 3 arc-faults.
not sure if it has something to do with the arc-fault or the jumper between panels or what.
everything is wired correctly. it holds on a normal breaker forever, holds on the arc fault until any load is applied.