This issue is not seen on gluster build: 3.7.9-10.

Here are the steps that were followed,

1. created a single brick distribute volume.
2. created 10 files on the mount point say 1 to 10.
3. added one more brick from a peer node and started rebalance. 
4. once the migration is completed, checked the file distribution in the backend. 

Checked the rebalance logs for both the nodes and the file migration has happened only once.

Also, above mentioned steps were done for a distributed volume with multiple bricks and as expected file distribution has happened only once.

Thanks Prasad.

Based on comment#3, I am closing this BZ.