I bought NAPA axles, 1 new & 1 reman. They came w/ same instruct sht. pg 5, top.
"NOTE: To avoid having any parts of the differential gears become mislocated, do not remove both drive axles at the same time. Complete the removal and reinstallation of one axle before removing the second."

I'm sure I read similar somewhere else as well, but can't recall where now. But it seems like it is consistant w/ your explanation/fix.