negative offset parameter expansion

Configuration Information [Automatically generated, do not change]:
Machine: i386
OS: linux-gnu
Compiler: gcc
Compilation CFLAGS:  -DPROGRAM='bash' -DCONF_HOSTTYPE='i386' 
-DCONF_OSTYPE='linux-gnu' -DCONF_MACHTYPE='i386-pc-linux-gnu' 
-DCONF_VENDOR='pc' -DSHELL -DHAVE_CONFIG_H  -I.  -I../bash -I../bash/include 
-I../bash/lib  -g -O2
uname output: Linux compi 2.4.26 #5 Fr Jun 4 21:43:44 CEST 2004 i686 GNU/Linux
Machine Type: i386-pc-linux-gnu

Bash Version: 2.05b
Patch Level: 0
Release Status: release

Description:
        Parameter expansion with negative offset does not work

Repeat-By:
        export bla=bla.WaV
        echo ${bla:-3}

        This should deliver "WaV", following the manpage, but I get "bla.WaV"