Works for me on 4.8.1. Try to delete the var/cache directory manually
Baffled by this, always made this modification with ease, I have removed any sign of checked="checked" in select_popup.tpl located in /public_html/design/backend/templates/common, cleared the cache multiple times + deleted the /public_html/var/cache/templates/backend folder also - but the checkboxes remain checked!
Try deleting all folders in /var/cache/.
If you use old admin panel on new CS-Cart version, please edit the following file
design/backend/templates/addons/old_adminpanel/overrides/common/select_popup.tpl
Finally yes! Thank you ecom labs that is what has gone on!
You are welcome!