Yeah, even with the swap, it still *deletes* the thumbnail sent by calibre, and we end up with the default thumb ;/. Sorry about that...
One thing I missed, though: KindleGen seems to systematically put the thumbnail over/after the resources count, and as the last resource:
KG:
KF8 unknown count (125): 0
KF8 thumbnail URI (129): 'kindle:embed:000B'
KF8 resources (images/fonts) count (131): 10
coveroffset (201): 9
thumboffset (202): 11
Calibre:
KF8 unknown count (125): 0
KF8 thumbnail URI (129): 'kindle:embed:0001'
KF8 resources (images/fonts) count (131): 11
coveroffset (201): 0
thumboffset (202): 1
----
KG:
KF8 unknown count (125): 0
KF8 thumbnail URI (129): 'kindle:embed:0003'
KF8 resources (images/fonts) count (131): 2
coveroffset (201): 1
thumboffset (202): 3
Calibre:
KF8 unknown count (125): 0
KF8 thumbnail URI (129): 'kindle:embed:0002'
KF8 resources (images/fonts) count (131): 3
coveroffset (201): 1
thumboffset (202): 2
----
KG:
KF8 unknown count (125): 0
KF8 thumbnail URI (129): 'kindle:embed:0009'
KF8 resources (images/fonts) count (131): 8
coveroffset (201): 5
thumboffset (202): 9
Calibre:
KF8 unknown count (125): 0
KF8 thumbnail URI (129): 'kindle:embed:0004'
KF8 resources (images/fonts) count (131): 7
coveroffset (201): 3
thumboffset (202): 4
I'm getting a bit cross eyed, so I'll look into that tomorrow
.