DirectoryInfo.GetFiles Method (String, SearchOption)

I've made three extension for the DirectoryInfo object, so that the match when using something like "*.abc" ONLY returns files with abc extension.

/// <summary>
            /// Returns a file list from the current directory matching the given searchPattern and using a value to determine whether to search subdirectories.
            /// This is as fix for 8.3 filename standard. more information here: http://msdn.microsoft.com/en-us/library/ms143327.aspx
            /// </summary>
            /// <param name="directoryinfo">object to use.</param>
            /// <param name="searchPattern">The search string, such as "System*", used to search for all directories beginning with the word "System".</param>
            /// <param name="searchOption">One of the values of the System.IO.SearchOption enumeration that specifies whether the search operation should include only the current directory or should include all subdirectories.</param>
            /// <returns>An array of type System.IO.FileInfo.</returns>
            /// <exception cref="System.ArgumentNullException">searchPattern is null.</exception>
            /// <exception cref="System.IO.DirectoryNotFoundException">The path is invalid, such as being on an unmapped drive.</exception>
            /// <exception cref="System.Security.SecurityException">The caller does not have the required permission.</exception>
            /// <remarks>http://msdn.microsoft.com/en-us/library/ms143327.aspx</remarks>
            public static FileInfo[] GetFilesFixed(this DirectoryInfo directoryinfo, string searchPattern, SearchOption searchOption)
            {
                if (((searchPattern.Length - (searchPattern.LastIndexOf('.') + 1)) == 3) && !searchPattern.Substring(searchPattern.LastIndexOf('.')).Contains('*'))
                    return directoryinfo.GetFiles(searchPattern, searchOption).ToList().FindAll(F => F.Extension.Length == 4).ToArray();
                return directoryinfo.GetFiles(searchPattern, searchOption);
            }

            /// <summary>
            /// Returns a file list from the current directory matching the given searchPattern.
            /// This is as fix for 8.3 filename standard. more information here: http://msdn.microsoft.com/en-us/library/ms143327.aspx
            /// </summary>
            /// <param name="directoryinfo">object to use.</param>
            /// <param name="searchPattern">The search string, such as "*.txt".</param>
            /// <returns>An array of type System.IO.FileInfo.</returns>
            /// <exception cref="System.ArgumentNullException">searchPattern is null.</exception>
            /// <exception cref="System.IO.DirectoryNotFoundException">The path is invalid, such as being on an unmapped drive.</exception>
            /// <exception cref="System.Security.SecurityException">The caller does not have the required permission.</exception>
            /// <remarks>http://msdn.microsoft.com/en-us/library/ms143327.aspx</remarks>
            public static FileInfo[] GetFilesFixed(this DirectoryInfo directoryinfo, string searchPattern)
            {
                if (((searchPattern.Length - (searchPattern.LastIndexOf('.') + 1)) == 3) && !searchPattern.Substring(searchPattern.LastIndexOf('.')).Contains('*'))
                    return directoryinfo.GetFiles(searchPattern).ToList().FindAll(F => F.Extension.Length == 4).ToArray();
                return directoryinfo.GetFiles(searchPattern);
            }

            /// <summary>
            /// Retrieves an array of strongly typed System.IO.FileSystemInfo objects representing the files and subdirectories matching the specified search criteria.
            /// This is as fix for 8.3 filename standard. more information here: http://msdn.microsoft.com/en-us/library/ms143327.aspx
            /// </summary>
            /// <param name="directoryinfo">object to use.</param>
            /// <param name="searchPattern">The search string, such as "System*", used to search for all directories beginning with the word "System".</param>
            /// <returns>An array of strongly typed FileSystemInfo objects matching the search criteria.</returns>
            /// <exception cref="System.ArgumentNullException">searchPattern is null.</exception>
            /// <exception cref="System.IO.DirectoryNotFoundException">The path is invalid, such as being on an unmapped drive.</exception>
            /// <exception cref="System.Security.SecurityException">The caller does not have the required permission.</exception>
            public static FileSystemInfo[] GetFileSystemInfosFixed(this DirectoryInfo directoryinfo, string searchPattern)
            {
                if (((searchPattern.Length - (searchPattern.LastIndexOf('.') + 1)) == 3) && !searchPattern.Substring(searchPattern.LastIndexOf('.')).Contains('*'))
                    return directoryinfo.GetFileSystemInfos(searchPattern).ToList().FindAll(F => F.Extension.Length == 4).ToArray();
                return directoryinfo.GetFiles(searchPattern);
            }