I have been fiddling on with various BIOS updates to see if I can reproduce this.
Initially the 3 machines I tried on were at BIOS 53 and I updated straight to 67.
BIOS versions available from Intel website:
52, 53, 54, 55, 57, 60, 61, 62, 64, 65, 66, 67.
53 -> 67 = flapping.
67 -> 53 blacklisted.
67 -> 54 failed.
67 -> 55 OK and no flapping.
55 -> 57 OK and no flapping.
57 -> 60 OK and no flapping.
60 -> 61 OK and no flapping.
61 -> 62 OK and no flapping.
62 -> 64 OK and no flapping.
64 -> 65 OK and no flapping.
65 -> 66 OK and no flapping.
66 -> 67 OK and no flapping.
67 -> 55 -> 67 OK and no flapping.
I have left the Windows driver untouched during all of this.
These BIOS updates were all done via the Windows .exe file.
I have another DQ67SW on the shelf so may start a fresh with that one next - it is still BIOS 53.
The CMD prompt ping seems to result in the same response every time - even on a flapping board. Just to restate - the flapping only happens when the PC is not running and Windows has been shutdown, but still powered - so it can be WoL. I have not tried sleep/hibernate.
I'll fiddle on with various other combinations - but any pointers at this stage would be good.
Upon further investigation - one the BIOS updates has disabled the Intel AMT. In the BIOS it reports firmware version 0.0.0.0
I have tried various options to get it reinstated - but no luck yet. Any suggestions?
In Windows device manager the Intel AMT SOL driver has a yellow triangle with 'cannot start (code 10)'.
I suspect once this is resolved the flapping will return.
I'll try and spend more time on it next week.
The other 2 boards are still flapping. If I cannot resolve this board I'll start again on another and watch it more carefully at each BIOS update.