Some Files in /usr/share/applications/ Not Displaying Icons in Thunar

**Debian Buster; Xfce version 4.12; Thunar version 1.8.4** In my /usr/share/applications/ directory (using **Thunar**), there are three .desktop file listings that do not display the correct icon. It is interesting to note that said three .desktop files are the only ones in said directory that stipulate the icon file in the below fashion (what follows are copies of each subject .desktop file's Icon=... line): Icon=ca.desrt.dconf-editor Icon=org.gnome.Evince Icon=org.gnome.Yelp It is also interesting to note that the correct icons appear in the **Xfce** whisker menu. For each of these three cases, I am able to find multiple instances of the proper icons in (and only in) the /usr/share/icons/hicolor directory. In addition, all of the non-affected .desktop files in said /usr/share/applications/ directory specify specific icon paths or a generic icon name (e.g. Icon=xfwm4). I have updated the relevant icon cache (using, as root, gtk-update-icon-cache -f /usr/share/icons/hicolor/) with no joy. I'm currently using the **Tango** icon theme in **Xfce** and do not wish to change that setting. I realize that, as a workaround, I could simply specify a path to the desired icon in each of the three subject .desktop files, but am curious as to what the problem could be?