Failure of nested substring processing inside double-quotes

lsb_release -rd:
Description: Ubuntu 14.04.1 LTS
Release: 14.04

apt-cache policy dash
dash:
  Installed: 0.5.7-4ubuntu1
  Candidate: 0.5.7-4ubuntu1
  Version table:
 *** 0.5.7-4ubuntu1 0
        500 http://us.archive.ubuntu.com/ubuntu/ trusty/main amd64 Packages
        100 /var/lib/dpkg/status

FYI, I reported the bug below on the dash mailing list and got this response from Herbert Xu:

> This is already fixed in the current git tree, by the commit:
>
> commit a7c21a6f4cb42d967854cae954efd4ee66bdea9c
> Author: Herbert Xu <email address hidden>
> Date: Fri Aug 23 20:04:12 2013 +1000
>
> [EXPAND] Propagate EXP_QPAT in subevalvar

I checked dash_0.5.8-1_amd64.deb from Debian experimental and this bug seems to be fixed there as well (but still broken in Debian sid, where the current version is dash_0.5.7-4_amd64.deb).

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Hi all. I recently found a bug in dash's handling of substring
processing, when the variable is contained within quotes.

In bash, this works:

  bash$ echo $PWD
  /home/psmith

  bash$ echo ${PWD%${PWD##*/}}.
  /home/.

  bash$ echo "${PWD%${PWD##*/}}."
  /home/.

which is what I expect. However, in dash we get:

  dash$ echo $PWD
  /home/psmith

  dash$ echo ${PWD%${PWD##*/}}.
  /home/.

  dash$ echo "${PWD%${PWD##*/}}."
  .

Whoops! Inside double-quotes dash is mishandling the nested string
substitution. If I break it up into two steps it works OK, regardless
of whether or not it's quoted.