`aptitude changelog apt` results in W: chmod 0700 of directory failed - SetupAPTPartialDirectory (1: Operation not permitted)

[Norbert]

Steps to reproduce:
1. Install Ubuntu 16.04 LTS
2. Install aptitude
3.1. Try to get changelog of the package:
$ aptitude changelog aptitude
3.1. Launch aptitude interactively with `sudo aptitude`, select package and click <C>

Expected results:
* changelog is shown, no errors or warning messages shown

Actual results:
a. changelog and warning message are shown:

$ aptitude changelog aptitude
Get: Changelog of aptitude
W: chmod 0700 of directory /var/lib/apt/lists/partial failed - SetupAPTPartialDirectory (1: Operation not permitted)
W: chmod 0700 of directory /var/cache/apt/archives/partial failed - SetupAPTPartialDirectory (1: Operation not permitted)

b. got warning "window" with text:

W: Can't drop privileges for downloading as file '/tmp/aptitude-root.13632:1pMX1q/aptitudeDownload6J+8J:+PsVGmTNm^.^::Lz:%.Hi55VKA' couldn't be
accessed by user '_apt'. - pkgAcquire::Run (13: Permission denied)

then read changelog.

Notes:
1. Directory rights are as follows:

$ sudo ls -ald /var/lib/apt/lists/partial /var/cache/apt/archives/partial
drwx------ 2 _apt root 4096 мар 2 18:18 /var/cache/apt/archives/partial
drwx------ 2 _apt root 24576 мар 2 18:22 /var/lib/apt/lists/partial

2. Ubuntu 14.04 LTS, 17.10 and 18.04 LTS are not affected by this bug.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: aptitude 0.7.4-2ubuntu2
ProcVersionSignature: Ubuntu 4.4.0-116.140-generic 4.4.98
Uname: Linux 4.4.0-116-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.15
Architecture: amd64
CurrentDesktop: MATE
Date: Fri Mar 2 18:22:18 2018
InstallationDate: Installed on 2018-01-04 (56 days ago)
InstallationMedia: Ubuntu 16.04 LTS "Xenial Xerus" - Release amd64 (20160420.1)
SourcePackage: aptitude
UpgradeStatus: No upgrade log present (probably fresh install)