Support

When you uninstall a component, Joomla! deletes all the component files including those in the media directory. Therefore reinstalling the component after uninstalling it should replace all files, including the ones that appear broken. Since this does not happen the only reasonable explanation is that these files have ended up with the wrong permissions and do not get deleted on uninstallation.

Retry the uninstallation and check specifically for these files. If they are present delete them. Now reinstall the component.

If this did not help think whether you are transferring these files by FTP or whether your site has the FTP mode in Global Configuration enabled. Some FTP servers may end up transferring files in ASCII mode which may change their line endings, therefore changing their size and their MD5 and SHA-1 signatures therefore triggering Admin Tools broken installation warning. Your host should be able to tell you if that is the case.

If you are receiving the same message about the same files without using FTP it's time to call your host. The other explanation of files "suddenly" deciding to change size is something running on your host which alters files without asking you. This would indeed be a problem, one of the problems our broken installation warning was specifically designed to detect (if you modify our code we can no longer guarantee that our software functions as designed and intended).