Position of left-tiled windows not restored correctly when another left-tiled window present

When another window is maximized or tiled to the left side of the screen, re-opening an application whose window was previously tiled to the left side does not restore that windows' previous position. Instead such windows open at varying distances from the dock, untiled.

= Steps to reproduce *expected* behavior (with a newly created user) =

1. open Firefox, drag the window to the left edge of the screen to tile it there (filling up the left half of horizontal screen space)
2. close Firefox
3. open Nautilus, make sure that the window floats (i.e. is unmaximized and not tiled to either side of screen)
4. open Firefox

== What happens ==
As expected, Firefox's window is tiled to the left edge of screen, immediately to the right side of the dock.

= Steps to reproduce *unexpected* behavior (with a newly created user) =
1. open Firefox, drag the window to the left edge of the screen to tile it there (filling up the left half of horizontal screen space)
2. close Firefox
3. open Nautilus, *maximize its window*
4. open Firefox

== What happens ==
Firefox's window opens slightly to the right off the right edge of the dock (with a gap between the dock and the window).
== What I expect to happen ==
I expect Firefox's window to be tiled to the left edge of screen, immediately to the right side of the dock, just as it did following the first recipe above.

= Further information =
Either maximizing or tiling Nautilus' window to the left edge of the screen (at step #3) triggers the issue. Tiling it to the *right* edge of the screen does not.

Using Gnome Terminal instead of Nautilus triggers the issue just as well, I suspect any other application will though I've only systematically tested these two so far.

From battling with this in my daily use I also know that the distance of incorrectly restored windows from the dock varies: different applications open at different distances. The precise mechanics of this still elude me, though the distances do appear to be multiples of 25 pixels.

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: mutter 3.28.1-1ubuntu1
ProcVersionSignature: Ubuntu 4.15.0-20.21-generic 4.15.17
Uname: Linux 4.15.0-20-generic x86_64
ApportVersion: 2.20.9-0ubuntu7
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Sun Apr 29 16:32:37 2018
InstallationDate: Installed on 2016-10-13 (562 days ago)
InstallationMedia: Ubuntu-Server 16.04.1 LTS "Xenial Xerus" - Release amd64 (20160719)
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=fi_FI.UTF-8
 SHELL=/bin/bash
SourcePackage: mutter
UpgradeStatus: No upgrade log present (probably fresh install)