not able to ‘grant’ custom capability

i have successfully created all custom capabilities for my custom post type, but the edit_[pluralnameofCPT] won’t save. all other capabilities (publish_[pluralnameofCPT], edit_others_[pluralnameofCPT], etc) show up and i’m able to check “Grant” for each, and those save successfully. yet when i try to check “grant” of the edit_[pluralnameofCPT], and hit “update”… it remains unchecked. (doesn’t save)

I’ve tried granting this capability for admin, and for a custom role, and neither will save this setting.