I cannot reproduce this.
Does Exiftool still give warnings?
The _original files are created by ExifTool and deleted if the write operation completed successfully.
What kind of virus checker do you run?
Did you try another folder. I've asked to check for file system permissions, did you do that? Maybe ExifTool is not allowed to rename or delete files in this folder?
Create a new folder on your C: disk, copy the file there, repeat your test.
Always in include the IMatch log file and the contents of the ExifTool output panel. If there is trouble with your files, it will be logged there.
Or, make some changes to the file in the ECP and see what ExifTool reports.
If the data in the file is damaged, it will not work. ACDSee is quite bad at metadata and may ignore or even damage maker notes when copying them to a new file or re-saving a modified file.