I believe bluetooth stability problems were down to the Socket bluetooth card revision E...
Not matter what I did, bluetooth stack would lock up even with new cacko 1.23.
Anyway, I managed to buy a used CF bluetooth card (it's a PANBT0101M, no name brand), and I found it 100% reliable. Unlike the Socket card, it sticks out of the Z, not too far, but actually I find that preferable since previously had to partially take the Z out of the PDAir case to get the flush-fit Symbol card out.