When uninstalling MinGW, the uninstaller removes the entire directory tree, including any files the user may have put in there. This was first reported as bug #1444344.
The problem is, the installer doesn't currently keep track of the contents of each package as they are installed. So, there is no way to know which files can be safely removed at uninstall time.
Meanwhile, a solution is to only remove files that the uninstaller knows about, then warn the user that some files may still remain.
The text I choose for the warning is:
"MinGW was successfully removed from your computer. However, some files may still remain. Please check $INSTDIR for files that you wish to keep, move or delete."
I made two versions of the patch. In the first version, the warning is added to the final message box. In the second (which I like slightly better), I replaced the message box with a full finish page.