SpiderOak ONE, Groups, and Enterprise treat files on removable media differently from most files. If a file originates with removable media, then SpiderOak backup products will not move their copy of it to the deleted items bin when the removable media is not present.
On Windows, a drive is considered removable if the API function GetDriveType does not return DRIVE_FIXED. CD/DVD drives, USB & firewire devices, and mounted network shares are all treated as removable. If ONE moves its copy of files from removable media to the deleted items bin, that means that the media in question is not properly reporting itself to Windows via GetDriveType. This is a problem with the removable hardware, not with SpiderOak backup. We have seen cases of this but there is nothing that we can do.
On Mac, drives mounted under /Volumes are treated as removable. This is Mac's default location for external media.
On Linux, drives mounted on /run/media or /media are treated as removable. This is Linux's current and previous default locations for external media.
You may also want to review how removable media is selected for backup.