Backflushing Issue

I have a user who did Item Booking for a particular item recently and had 
a backflushing issue. 

When going into the Inventory Movements Inquiry they noticed that some of 
the parts in the routing backflushed and some didn't.  The interesting 
thing is that previous booking and subsequent bookings have worked just 
fine.  It's just this one particular instance that this problem occurred.

Does anyone have any ideas what might have happened or what the problem 
is?  I hate these once in a great while issues because it usually ends up 
being a user created problem.

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