Sorry to hear about your lost scripts, however this is not a bug, the mIRC uninstaller will always uninstall the last copy of mIRC that was run.

That is why when you attempt to uninstall, the uninstaller will always tell you which folder it is going to uninstall, giving you the option to cancel the operation.

Since there is only one registry entry in the Windows Control Panel Add/Remove section for mIRC, that entry is always updated by the most recently run mIRC, ensuring that no matter how many times you fiddle with installs or uninstalls, you will always be able to uninstall the last run copy of mIRC.