graphic bug for prompt in password field in qt5 application

In password field of qt5 application, (seen here with keepassxc and electrum), one can notice that following graphic bug:

When the input password field is empty, the prompt is a vertical bar.

But as soon as you type something in it, it becomes, something like a "flag" aka. a vertical bar with a little triangle at the top.

The added graphical artefact (the triangle) is not displayed at the same position, relative to the vertical bar, given the count of characters in the input field.

Meaning, the triangle is sometimes slightly off, and sometimes it is perfectly aligned on the vertical bar.

In the example screenshot, the triangle is not perfectly aligned with the vertical bar.

on ubuntu 18.10, using wayland, gnome-shell, qt5.11.1, intel hd card on i3-3217U (default driver)

with the same config, one does not see such a graphical bug on (current as of today) archlinux.

ProblemType: Bug
DistroRelease: Ubuntu 18.10
Package: libqt5core5a 5.11.1+dfsg-7ubuntu1
ProcVersionSignature: Ubuntu 4.18.0-11.12-generic 4.18.12
Uname: Linux 4.18.0-11-generic x86_64
NonfreeKernelModules: wl
ApportVersion: 2.20.10-0ubuntu13.1
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Wed Nov 21 23:30:55 2018
InstallationDate: Installed on 2018-05-07 (198 days ago)
InstallationMedia: Ubuntu 18.04 LTS "Bionic Beaver" - Release amd64 (20180426)
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=fr_FR.UTF-8
 SHELL=/bin/bash
SourcePackage: qtbase-opensource-src
UpgradeStatus: Upgraded to cosmic on 2018-10-19 (33 days ago)