Webmin is highly useful, but it has issues:
1) Module "Linux Firewall" produces correct IPtables config file, yet later IPtables blocks off outbound DNS (leading to, for example, ping google.com always failing). Sadly I've not used the module ever since so I don't remember other issues with the module.
2) Deleting Webmin modules with dependencies: like APT or aptitude you should be asked whether to delete or skip the depending modules. Having to delete modules one-by-one is the wrong way.
That should be done in any other module too.
3) Not exactly an issue, but Webmin installs loads of mostly unneeded modules and you have to uninstall them everytime you install Webmin, bearing the issue #2. Instead the modules should be available for installing locally, or just don't carry them with you at all. Not carrying drops the package size, but I think that's not problem usually.
When installing Webmin using the package, DEB in my case, the installer should check whether a module is installed and update if needed.
Am I being ignored here ?