PROMPT_DIRTRIM skips depth n-1 when ~ is n

[dennis]

Configuration Information [Automatically generated, do not change]:Machine: 
i486OS: linux-gnuCompiler: gccCompilation CFLAGS:  -DPROGRAM='bash' 
-DCONF_HOSTTYPE='i486' -DCONF_OSTYPE='lin$uname output: Linux emperor 
2.6.31-14-generic #48-Ubuntu SMP Fri Oct 16 14:04:2$Machine Type: 
i486-pc-linux-gnu
Bash Version: 4.0Patch Level: 33Release Status: release
Description:
If you are in a directory below ~ and you set PROMPT_DIRTRIM to the 
depthminus 2 it includes the depth minus 1 directory in the prompt as 
well.
Repeat-By:
$ mkdir -p /tmp/seven/six/five/four/three/two/one$ cd 
/tmp/seven/six/five/four/three/two/one$ PS1="\w$ 
"/tmp/seven/six/five/four/three/two/one$ 
PROMPT_DIRTRIM=0/tmp/seven/six/five/four/three/two/one$ 
PROMPT_DIRTRIM=1.../one$ PROMPT_DIRTRIM=2.../two/one$ 
PROMPT_DIRTRIM=3.../three/two/one$ PROMPT_DIRTRIM=4.../four/three/two/one$ 
PROMPT_DIRTRIM=5.../five/four/three/two/one$ 
PROMPT_DIRTRIM=6.../six/five/four/three/two/one$ 
PROMPT_DIRTRIM=7.../seven/six/five/four/three/two/one$ 
PROMPT_DIRTRIM=8/tmp/seven/six/five/four/three/two/one$ cd ~~$ mkdir -p 
~/seven/six/five/four/three/two/one~$ cd 
~/seven/six/five/four/three/two/one~/seven/six/five/four/three/two/one$ 
PROMPT_DIRTRIM=0~/seven/six/five/four/three/two/one$ 
PROMPT_DIRTRIM=1~/.../one$ PROMPT_DIRTRIM=2~/.../two/one$ 
PROMPT_DIRTRIM=3~/.../three/two/one$ 
PROMPT_DIRTRIM=4~/.../four/three/two/one$ 
PROMPT_DIRTRIM=5~/.../five/four/three/two/one$ 
PROMPT_DIRTRIM=6~/seven/six/five/four/three/two/one$

Repeated here without the prompts:
mkdir -p /tmp/seven/six/five/four/three/two/onecd 
/tmp/seven/six/five/four/three/two/onePS1="\w$ 
"PROMPT_DIRTRIM=0PROMPT_DIRTRIM=1PROMPT_DIRTRIM=2PROMPT_DIRTRIM=3PROMPT_DIRT
RIM=4PROMPT_DIRTRIM=5PROMPT_DIRTRIM=6PROMPT_DIRTRIM=7PROMPT_DIRTRIM=8cd 
~mkdir -p ~/seven/six/five/four/three/two/onecd 
~/seven/six/five/four/three/two/onePROMPT_DIRTRIM=0PROMPT_DIRTRIM=1PROMPT_DI
RTRIM=2PROMPT_DIRTRIM=3PROMPT_DIRTRIM=4PROMPT_DIRTRIM=5PROMPT_DIRTRIM=6