[Bug 1532944] [NEW] flashplugin-installer can't correctly install the downloaded package anymore with apt 1.1.x

[Sworddragon]

Public bug reported:

I'm using Ubuntu 16.04 dev with apt 1.1.10 and on trying to install
flashplugin-installer I'm noticing that the downloaded package can't be
correctly installed anymore. Here is an example output:

root at ubuntu:~# apt-get install flashplugin-installer --reinstall
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following packages were automatically installed and are no longer required:
  libapt-inst1.7 libapt-pkg4.16
Use 'apt autoremove' to remove them.
0 upgraded, 0 newly installed, 1 reinstalled, 0 to remove and 0 not upgraded.
Need to get 0 B/6838 B of archives.
After this operation, 0 B of additional disk space will be used.
debconf: delaying package configuration, since apt-utils is not installed
(Reading database ... 99770 files and directories currently installed.)
Preparing to unpack .../flashplugin-installer_11.2.202.559ubuntu1_amd64.deb ...
Unpacking flashplugin-installer (11.2.202.559ubuntu1) over (11.2.202.559ubuntu1) ...
Processing triggers for update-notifier-common (3.164) ...
flashplugin-installer: downloading http://archive.canonical.com/pool/partner/a/adobe-flashplugin/adobe-flashplugin_20151228.1.orig.tar.gz
Get:1 http://archive.canonical.com/pool/partner/a/adobe-flashplugin/adobe-flashplugin_20151228.1.orig.tar.gz [26.8 MB]
Fetched 26.8 MB in 3min 8s (143 kB/s)                                                                                                                                                                                                       
W: Can't drop privileges for downloading as file '/var/lib/update-notifier/package-data-downloads/partial/adobe-flashplugin_20151228.1.orig.tar.gz' couldn't be accessed by user '_apt'. - pkgAcquire::Run (13: Permission denied)
Installing from local file /var/lib/update-notifier/package-data-downloads/partial/adobe-flashplugin_20151228.1.orig.tar.gz
Flash Plugin installed.
Setting up flashplugin-installer (11.2.202.559ubuntu1) ...

** Affects: apt (Ubuntu)
     Importance: Undecided
         Status: New

** Affects: flashplugin-nonfree (Ubuntu)
     Importance: Undecided
         Status: New

** Also affects: apt (Ubuntu)
   Importance: Undecided
       Status: New

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https://bugs.launchpad.net/bugs/1532944

Title:
  flashplugin-installer can't correctly install the downloaded package
  anymore with apt 1.1.x

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