>>Who is destroying first: parent or child? I think you need to do something else, storing a reference to the parent in the child object referenced in the parent will put you in trouble (already did).
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>OK, I think I've found it - I was creating a reference to the child control in _screen.oCtl, which I cleared only when the object destroyed. It obviously doesn't run its .destroy(), for whichever reason, but now I've discovered I can remove this reference much earlier, so now it seems to work.

Good you found the cause of your problem. Too much intercourse between objects can definitely cause some grief later. <g>