Not necessarily 'mishandling' but different handling in some way to the other airlines. This was discussed way back when the thread was about battery problems.
I would presume that someone has done a very detailed study of implementation of the procedures to check for differences with the potential to change the way the batteries were charged, discharged or handled.
Even in the steel boxes a failure cannot be hidden away. There are considerably more 78's in service now all over the world. If there was a continuing battery issue I am certain those with anti-787 sentiment would be making all efforts to publicize them. So even without access to the battery change out records, one can assume that the multiple 'fixes' have been successful.