I accidentally found an interesting feature in Windows 2000 Server. The best way for you to see what happened is to follow a few simple steps:
You'll discover that both the Important.htm file and the Important_files folder have disappeared. The good news is that Microsoft is aware of this problem and addresses it in "Operations on an HTML File or Folder Apply to Similarly Named Folder or HTML File" (http://support.microsoft.com/support/kb/articles/q252/7/21.asp). The bad news is that this functionality is supposedly by design. The Microsoft article explains that if a folder has a specific appendix and a similarly named .htm or .html file exists at the same level as the folder, deleting the file causes the OS to delete the folder as well. The English language appendixes that cause this behavior are _files, _file, .files, filer, and _fails.
To fix this problem, use a registry editor to add the NoFileFolderConnection entry of type REG_DWORD with a value of 1 to the HKEY_CURRENT_USER\Software\Microsoft\Windows\Current-Version\Explorer subkey. This value disables the file connection.