Window buttons icon effect isn't applied to mutter decorations

This bug was fixed in the package mutter - 3.28.1-1

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mutter (3.28.1-1) unstable; urgency=medium

  [ Jeremy Bicha ]
  * New upstream release
    - Fix window button spacing when display is scaled (LP: #1725133)
  * Bump Standards-Version to 4.1.4

  [ Marco Trevisan (Treviño) ]
  * Add patches proposed upstream:
  * theme-frames-Use-surface-device-scale-instead-of-cairo_sc.patch:
    - theme, frames: Use surface device scale instead of cairo_scale
      (LP: #1764554)
  * theme-use-gtk_render_icon_suface-to-paint-button-icon.patch:
    - theme: use gtk_render_icon_suface to paint button icon
      (LP: #1764558)
  * theme-load-icons-as-Gtk-does-with-fallback-and-RTL-suppor.patch:
    - theme: load icons as Gtk does with fallback and RTL support
  * clutter-Smooth-out-master-clock-to-smooth-visuals.patch:
    - clutter: Smooth out master clock to smooth visuals
  * core-Return-1-if-meta_window_get_monitor-is-called-on-an-.patch:
    - core: Return -1 if meta_window_get_monitor is called on an
      unmanaged window (LP: #1724439)
  * backends-Move-MetaOutput-crtc-field-into-private-struct.patch:
    - backends: Move MetaOutput::crtc field into private struct
      (LP: #1703668)
  * backends-Add-logical-monitor-monitor-output-crtc-ref-chai.patch:
    - backends: Add logical monitor -> monitor -> output -> crtc ref
      chain (LP: #1703668)

 -- Jeremy Bicha <email address hidden> Mon, 16 Apr 2018 22:35:14 -0400

This patch is broken, and is responsible for re-introducing bug 1718238 (comment 17 onwards).

Egmont, you can file a bug and tag it regression-release

https://wiki.ubuntu.com/StableReleaseUpdates#Regressions

Done: bug 1770507.