When you click on the icon to Export the mod to a ZIP or JAR file and select the same file name on a drive you want to write to (basically overwrite existing), the file is not overwritten and there is a new file created with the name chosen with a second .jar in the name. (abcdeFGH.jar.jar) If a user wants to overwrite an existing file, they should be able to by being prompted with a dialog to confirm.
MCreator issue tracker has been migrated to GitHub.
Existing tickets have been migrated to GitHub. Please open new tickets on the GitHub tracker instead. If you do not have a GitHub account, all feature requests and bug reports from forums are still considered and checked by the maintainers.