Normally, Nextcloud detects moving and renaming operations and won’t transfer files again. I have seen problems in the past if the connections was interrupted and the client or server couldn’t be sure of the operation and re-transferred the file to be sure (or at least I interpreted it in this way).
If you can reproduce this error, you should first check your logfiles for errors, perhaps something is not configured correctly, you can also try on one of the demo instances: