installing graphviz-cairo breaks apt-get until script files are manually deleted

Binary package hint: graphviz-cairo

Basically, trying to install the graphviz-cairo plugin to graphvis using apt-get results in two shell script files sticking around in /var/lib/dpkg/info/ that apt-get keeps trying to run, so apt-get can't install, remove, or update anything until the two script files are deleted manually.

I'm running Edgy, but I encountered this bug a year ago on Dapper beta and didn't report it. The fix is easy, but it's affected several people and come up at least three times on the forums:
http://ubuntuforums.org/showthread.php?p=2117662
http://www.ubuntuforums.org/showthread.php?t=365719
http://ubuntuforums.org/showthread.php?p=2190896

repro steps:
>sudo apt-get install graphviz-cairo

it should end like this:
Setting up graphviz-cairo (2.8-2) ...
/var/lib/dpkg/info/graphviz-cairo.postinst: 11: dot: not found
dpkg: error processing graphviz-cairo (--configure):
 subprocess post-installation script returned error exit status 127
Errors were encountered while processing:
 graphviz-cairo
E: Sub-process /usr/bin/dpkg returned an error code (1)

now, try using apt-get for just about anything else:
>sudo apt-get remove evolution
...
Removing evolution-plugins ...
Removing evolution-exchange ...
Removing evolution ...
Setting up graphviz-cairo (2.8-2) ...
/var/lib/dpkg/info/graphviz-cairo.postinst: 11: dot: not found
dpkg: error processing graphviz-cairo (--configure):
 subprocess post-installation script returned error exit status 127
Errors were encountered while processing:
 graphviz-cairo
E: Sub-process /usr/bin/dpkg returned an error code (1)

apt-get can't even uninstall graphviz-cairo and fix the problem:
>sudo apt-get remove graphviz-cairo
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages were automatically installed and are no longer required:
  graphviz-cairo
Use 'apt-get autoremove' to remove them.
The following packages will be REMOVED:
  graphviz-cairo
0 upgraded, 0 newly installed, 1 to remove and 1 not upgraded.
1 not fully installed or removed.
Need to get 0B of archives.
After unpacking 193kB disk space will be freed.
Do you want to continue [Y/n]? y
(Reading database ... 133226 files and directories currently installed.)
Removing graphviz-cairo ...
/var/lib/dpkg/info/graphviz-cairo.postrm: 11: dot: not found
dpkg: error processing graphviz-cairo (--remove):
 subprocess post-removal script returned error exit status 127
Errors were encountered while processing:
 graphviz-cairo
E: Sub-process /usr/bin/dpkg returned an error code (1)

On the other hand, the fix is quite simple.
>sudo rm /var/lib/dpkg/info/graphviz-cairo.post*
allows apt-get to work, and
>sudo aptitude remove -f graphviz-cairo
then removes the offending plugin.

The problem seems to me to be two script files, /var/lib/dpkg/info/graphviz-cairo.postinst and /var/lib/dpkg/info/graphviz-cairo.postrm
I know almost nothing about shell scripting, but they seem very broken. This is graphviz-cairo.postinst: (some spaces removed)
#!/bin/sh

set -e

case "$1" in
    configure)
  dot -c
    ;;
esac

exit 0

and graphviz-cairo.postrm is almost identical:
>diff /var/lib/dpkg/info/graphviz-cairo.post*
8,9c8,9
< configure)
< dot -c
---
> remove)
> dot -c

I have no experience with this, but this seems like a somewhat serious bug that should also be (relatively) quite easy to fix.