When you delete a file, one of the choices is "Remove from Media Library and send to the Recycle Bin".
If the files reside on a non-Windows based system, such as a Linux-running NAS, the recycle bin will permanently delete the files, since the NAS will not have a recycle bin that MC understands. Are your files locally stored?
Network drives never have a Recycle Bin, even when accessed through Windows Explorer.