GDB uses the GNU `readline' library which has its own init file.
On MS-DOS this file is "/inputrc".  However, the code that reads
it requires that the value returned by `read' is exactly the size
of the file as reported by `stat'.  This means that if you edit
the file with a DOS editor, the contents of file will be ignored
as if it cannot be read.

The following patch solves the problem.

*** readline/readline.c~1       Fri Jan 12 18:24:20 1996
--- readline/readline.c Sun May  5 18:09:28 1996
*************** rl_read_init_file (filename)
*** 5765,5772 ****
--- 5765,5778 ----
    i = read (file, buffer, finfo.st_size);
    close (file);

+ #ifdef __MSDOS__
+   if (i < 0)
+     return (errno);
+   finfo.st_size = i;
+ #else
    if (i != finfo.st_size)
      return (errno);
+ #endif

    /* Loop over the lines in the file.  Lines that start with `#' are
       comments; all other lines are commands for readline initialization. *

This bug is fixed in the rdln22[bs].zip distribution.