Nah, it's more like not all deletions are equal. It probably has to do with the user launching the event on the backend, if I were to guess, but sometimes if you delete something through Explorer, it isn't added to the undo history. Some of these I've seen not end up in the recycle bin despite not permanently deleting them, hence why I wouldn't be surprised if it was another user being used for these edge-cases. The deleted items would then be added to that user's recycle bin and be unavailable to the actual user's undo history.

Basically; not really sure, just making a wild guess, but I've encountered similar edge-cases before.