Bug#776434: gnuplot: Installing both gnuplot and gnuplot5 breaks gnuplot4 help

[Antonio Ospite]

Package: gnuplot
Version: 4.6.6-1
Severity: important

Dear Maintainer,

when installing both gnuplot and gnuplot5 the gnuplot4 help is broken
with this error:

--------------------------------------------------------------------
$ gnuplot4

        G N U P L O T
        Version 4.6 patchlevel 6    last modified September 2014
        Build System: Linux x86_64

        Copyright (C) 1986-1993, 1998, 2004, 2007-2014
        Thomas Williams, Colin Kelley and many others

        gnuplot home:     http://www.gnuplot.info
        faq, bugs, etc:   type "help FAQ"
        immediate help:   type "help"  (plot window: hit 'h')

Terminal type set to 'qt'
gnuplot> help
/usr/share/gnuplot/gnuplot.gih: No such file or directory
gnuplot>
--------------------------------------------------------------------

To reproduce that just install gnuplot, then install gnuplot5 and then
try using the 'help' command from gnuplot4.

I am not sure if this is a bug in gnuplot or gnuplot5 but I am filing it
here because gnuplot4 is the broken package.

Thanks,
   Antonio

-- System Information:
Debian Release: 8.0
  APT prefers unstable
  APT policy: (900, 'unstable')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 3.19.0-rc5-ao2 (SMP w/1 CPU core)
Locale: LANG=it_IT.utf8, LC_CTYPE=it_IT.utf8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/bash
Init: systemd (via /run/systemd/system)

Versions of packages gnuplot depends on:
ii  gnuplot-qt [gnuplot-x11]  4.6.6-1

gnuplot recommends no packages.

Versions of packages gnuplot suggests:
ii  feedgnuplot              1.34-2
pn  gnuplot-doc              <none>
pn  libgnuplot-iostream-dev  <none>
pn  python-gnuplot           <none>

-- no debconf information
-- 
Antonio Ospite
http://ao2.it

A: Because it messes up the order in which people normally read text.
   See http://en.wikipedia.org/wiki/Posting_style
Q: Why is top-posting such a bad thing?