At the start of an upgrade or install terminal shows GLib-CRITICAL **: g_child_watch_add_full: assertion 'pid>0' failed (tagged synaptic:2XXXX)

[Robin]

This bug exists in Trusty T, but not in Saucy S. Synaptic is not rendered dysfunctional, but some piece of logic or coding is clearly faulty!

It is easiest to spot when installing a single package, using the terminal, and not closing the terminal on completion.

Description: Ubuntu Trusty Tahr (development branch)
Release: 14.04
synaptic:
  Installed: 0.80.4
  Candidate: 0.80.4
  Version table:
 *** 0.80.4 0
        500 http://gb.archive.ubuntu.com/ubuntu/ trusty/universe amd64 Packages
        100 /var/lib/dpkg/status
Expected: terminal output relating to packages being installed, with no error messages
What happened instead: The first line of terminal output is an error message, *for example*:
(synaptic:22582) GLib-CRITICAL **: g_child_watch_add_full: assertion 'pid>0' failed
or
(synaptic:25866) GLib-CRITICAL **: g_child_watch_add_full: assertion 'pid>0' failed
or
(synaptic:20621) GLib-CRITICAL **: g_child_watch_add_full: assertion 'pid>0' failed

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Nicolas DERIVE (kalon33)]

Still present in latest Synaptic version (0.81.1)