Both Arch Linux (plasma 5.14 beta) and neon dev unstable are affected. Spinboxes and text fields are borderless in desktop settings, task manager settings and widgets settings. You can see several screenshots in the following link http://imgbox.com/g/sWXa872xzm
Yes, I can confirm this issue on Arch Linux.
Can I see the output of "env" and running plasmashell from a terminal please
GS_LIB=/home/stalker/.fonts KDE_FULL_SESSION=true LANG=pt_BR.UTF-8 PROFILEHOME= DISPLAY=:1 SHELL_SESSION_ID=3c5ad5207e504fbfbfeb1179989e194e COLORTERM=truecolor MOZ_PLUGIN_PATH=/usr/lib/mozilla/plugins XDG_VTNR=2 PAM_KWALLET5_LOGIN=/run/user/1000/kwallet5.socket XDG_SESSION_ID=2 USER=stalker DESKTOP_SESSION=/usr/share/wayland-sessions/plasmawayland KONSOLE_VERSION=180801 WAYLAND_DISPLAY=wayland-0 PWD=/home/stalker HOME=/home/stalker XCURSOR_SIZE=0 XDG_SESSION_TYPE=wayland XDG_DATA_DIRS=/home/stalker/.local/share/flatpak/exports/share:/var/lib/flatpak/exports/share:/usr/local/share:/usr/share:/var/lib/snapd/desktop KONSOLE_DBUS_SESSION=/Sessions/2 XDG_SESSION_DESKTOP=KDE KONSOLE_DBUS_WINDOW=/Windows/1 QT_WAYLAND_FORCE_DPI=96 MAIL=/var/spool/mail/stalker TERM=xterm-256color SHELL=/bin/bash KONSOLE_DBUS_SERVICE=:1.51 XDG_SESSION_CLASS=user XDG_SEAT_PATH=/org/freedesktop/DisplayManager/Seat0 XCURSOR_THEME=breeze_cursors XDG_CURRENT_DESKTOP=KDE KONSOLE_PROFILE_NAME=Perfil 1 QT_WAYLAND_DISABLE_WINDOWDECORATION=1 XDG_SEAT=seat0 SHLVL=3 COLORFGBG=15;0 LANGUAGE=pt_BR:en_US:pt_BR WINDOWID=1 PLASMA_USE_QT_SCALING=1 LOGNAME=stalker DBUS_SESSION_BUS_ADDRESS=unix:abstract=/tmp/dbus-fTGbzzECRr,guid=c8951d1318c4059275e6c7a25b9fc1b7 XDG_RUNTIME_DIR=/run/user/1000 XDG_SESSION_PATH=/org/freedesktop/DisplayManager/Session1 QT_AUTO_SCREEN_SCALE_FACTOR=0 PATH=/usr/local/sbin:/usr/local/bin:/usr/bin:/var/lib/flatpak/exports/bin:/usr/lib/jvm/default/bin:/usr/bin/site_perl:/usr/bin/vendor_perl:/usr/bin/core_perl:/var/lib/snapd/snap/bin KDE_SESSION_UID=1000 KDE_SESSION_VERSION=5 SESSION_MANAGER=local/Arch-PC:@/tmp/.ICE-unix/585,unix/Arch-PC:/tmp/.ICE-unix/585 _=/usr/bin/env
Looks like Breeze also has QtQuick Controls special cases for SpinBoxes. I can no longer reproduce after fixing Bug 398663 *** This bug has been marked as a duplicate of bug 398663 ***