readline inserts bogus newline for some prompt lengths

[Alexey Toptygin]

Configuration Information [Automatically generated, do not change]:
Machine: i486
OS: linux-gnu
Compiler: gcc
Compilation CFLAGS:  -DPROGRAM='bash' -DCONF_HOSTTYPE='i486' 
-DCONF_OSTYPE='linux-gnu' -DCONF_MACHTYPE='i486-pc-linux-gnu' 
-DCONF_VENDOR='pc' -DLOCALEDIR='/usr/share/locale' -DPACKAGE='bash' -DSHELL 
-DHAVE_CONFIG_H   -I.  -I../bash -I../bash/include -I../bash/lib   -g -O2
uname output: Linux rain.foo 2.6.16-2-686 #2 Mon May 22 23:10:59 UTC 2006 i686 
GNU/Linux
Machine Type: i486-pc-linux-gnu

Bash Version: 3.1
Patch Level: 17
Release Status: release

Description:
        The builtin readline in bash inserts an unneeded newline at the
        end of the prompt if the prompt is $COLUMNS * n + 1 characters.
        If n is 1 and you backspace to the beginning of the line, the
        prompt creeps down 1 line.

Repeat-By:
        export COLUMNS;
        PS1=`perl -e 'print ( q/-/ x ($ENV{COLUMNS} * 1 + 0));'`;
        <type some commands, backspace to beginning of line>
        PS1=`perl -e 'print ( q/-/ x ($ENV{COLUMNS} * 1 + 1));'`;
        <type some commands, backspace to beginning of line>
        PS1=`perl -e 'print ( q/-/ x ($ENV{COLUMNS} * 1 + 2));'`;
        <type some commands, backspace to beginning of line>
        PS1=`perl -e 'print ( q/-/ x ($ENV{COLUMNS} * 2 + 0));'`;
        <type some commands, backspace to beginning of line>
        PS1=`perl -e 'print ( q/-/ x ($ENV{COLUMNS} * 2 + 1));'`;
        <type some commands, backspace to beginning of line>
        PS1=`perl -e 'print ( q/-/ x ($ENV{COLUMNS} * 2 + 2));'`;
        <type some commands, backspace to beginning of line>

Fix:
        Don't know readline internals, sorry :-/

                        Alexey