[WP Smush Pro] WP Smush Pro smushing original images

Dear Sir,
I am working on a stock photography website with over two thousand images. As you are aware in stock photography after a customer makes a purchase a digital downloadable link is provided which allows the purchaser to download the full resolution image. When an image is uploaded various thumbnails automatically generated. I had installed WP Smush Pro today with the objective of reducing the file size of all thumbnail images without any alteration of the original uploads. I had kept the option " Smush my original full size images" off so that my original uploads are untouched. Now when i ran the Bulk Smush option the plugin started to smush all images including the original uploads and reduced file sizes drastically. I had to abort the process and by the time 30 original images had already been smushed. I have to delete those images and re-upload them again.
Any suggestions in this regard is highly appreciated.
Thanking you.
Roop Dey