I guess we can assume it was either the bearing seals settling in or the position of the bearings in the hub settling very slightly. The latter does seem to be a bit of a judgement call in setting the position of the outer race while fitting it up to the hub centre spacer between the two inner races.
I guess, as I really didn't do anything different the second time around? Nothing seemed amiss when I dismantled it. I really can't believe the bearings can be 'seated' by just tightening up the axle nut, so I'm thinking there was something up between that inner spacer inside the hub, and/or the inner bearing? I'll chalk it up to dumb luck this time, or was that dumb #$! who messed it up the first time (me). J