Compiz slightly blurry titlebar font when window is not maximized

I've configured Compiz to use gtk-window-decorator so that it may apply my Metacity theme for the titlebars. With this decorator, I've noticed that Compiz renders slightly blurry titlebar fonts when a window is not maximized. Once the window is maximized, sharp fonts are rendered.

When a window is not maximized, the font has a lighter color and seems to lack subpixel hinting or anti-aliasing, hence the slightly blurry appearance. I zoomed in on the font when the window was maximized and observed bluish lines around the characters. When a window was not maximized, the zoomed-in characters didn't have the bluish lines.

I've tested and seen that the Marco window manager (forked from Metacity for the MATE desktop environment) and the Emerald decorator (used with Compiz) both render sharp titlebar fonts regardless of whether a window is maximized or not.

Could this be caused by a lack of subpixel hinting or anti-aliasing in gtk-window-decorator when a window is not maximized?

The image in the below link shows the slight difference in font rendering when Compiz is used with gtk-window-decorator. Firefox's window was maximized, with sharp text, while VLC's window was not maximized, with slightly blurry text.

https://i.stack.imgur.com/5BalZ.png

Upon switching to Marco window manager, both texts are sharp.

https://i.stack.imgur.com/9Gzli.png

When the "Compiz with gtk-window-decorator" setup is zoomed-in, blue lines around the maximized Firefox window titlebar text are visible (it looks like subpixel rendering to me). The blue lines are completely lacking in the un-maximized VLC window titlebar text.

https://i.stack.imgur.com/XDSAU.png

Testing with different Metacity themes has the same slightly blurry result. It seems to be a window decorator issue.

System Details
-----------------
I'm running Ubuntu-MATE 18.04 with the latest packages.

$ uname -a

Linux adminpc 4.15.0-23-generic #25-Ubuntu SMP Wed May 23 18:02:16 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux

$ lsb_release -crid

Distributor ID: Ubuntu
Description: Ubuntu 18.04 LTS
Release: 18.04
Codename: bionic

$ apt-cache show compiz

Package: compiz
Architecture: all
Version: 1:0.9.13.1+18.04.20180302-0ubuntu1
Priority: optional
Section: universe/x11
Origin: Ubuntu
Maintainer: Ubuntu Developers <email address hidden>
Original-Maintainer: Debian X Strike Force <email address hidden>
Bugs: https://bugs.launchpad.net/ubuntu/+filebug
Installed-Size: 111
Provides: x-window-manager
Depends: compiz-core (>= 1:0.9.13.1+18.04.20180302-0ubuntu1), compiz-plugins-default (>= 1:0.9.13.1+18.04.20180302-0ubuntu1), compiz-gnome
Filename: pool/universe/c/compiz/compiz_0.9.13.1+18.04.20180302-0ubuntu1_all.deb
Size: 3940
MD5sum: c9475c934a59c2846efe0aa00670a14c
SHA1: 7ac9879a61117f54c25ced64adbfac088ae5c5a9
SHA256: 9d6d0c01c6b8d699ec71c4c6081e937fca2998d9dbe537309caca86c3dcf532d
Homepage: https://launchpad.net/compiz
Description-en: OpenGL window and compositing manager
 Compiz brings to life a variety of visual effects that make the Linux desktop
 easier to use, more powerful and intuitive, and more accessible for users
 with special needs.
 .
 This metapackage provides the components necessary for running compiz. It
 provides the compiz core, a set of standard plugins, a window decorator using
 the Gtk toolkit and the files necessary to integrate compiz with the GNOME
 desktop environment.
Description-md5: f8949ff691855a5244d51aa54ee72f8f
Task: ubuntu-mate-desktop
Supported: 3y