BACKFILL_nn table includes mutations prior to running an import

When the BACKFILL_nn table is imported it also includes mutations which occurred prior to running the import command. But the documentation indicates:

BACKFILL_##
— Streams all key mutations for a given amount of time (in minutes).
For example, run the following import command to import the BACKFILL_2 table and mutations made in 2 minutes prior to running the command are also imported, not just the mutations made in the subsequent 2 minutes.

sqoop import -Dmapreduce.job.max.split.locations=2048 --connect http://10.0.2.15:8091/pools --table BACKFILL_2 --target-dir /backfill_dir --as-textfile