Reclaim disk space after dropping table(innodb_file_per_table = ON), strange scenario
I would recommend you to run the following 

mysqlcheck -u ROOTUSERNAME -p --auto-repair --optimize DBNAME_HERE


This will prompt for MySQL Root Password, type in and it will  reclaim the disk space. Time taken for this process will depend on the size of the database. You may try this first in your test env and then proceed.