OS: arch linux
Thunar 1.6.15

Hi, I've noticed several .desktop files not showing the correct icon when the desktop file references 'Icon=foo' and 'foo' is a string value containing a period (.) or several of those. This works as expected in Nautilus (which I don't use but installed to double-check this issue).

Realizing the wording here might not convey the issue very clearly, let me give an example.
The gnome-mpv desktop file has the following content:

https://github.com/gnome-mpv/gnome-mpv/blob/master/data/io.github.GnomeMpv.desktop.in

[Desktop Entry]
Version=1.0
Name=GNOME MPV
Comment=GTK+ frontend for mpv
Exec=gnome-mpv %U
# Translators: This is an icon name, don't translate!
Icon=io.github.GnomeMpv
Terminal=false
Type=Application
StartupNotify=true
StartupWMClass=Gnome-mpv
DBusActivatable=true
Categories=GTK;GNOME;AudioVideo;Player;Video;TV;
MimeType=application/mpeg4-iod;application/mpeg4-muxcodetable;application/mxf;application/ogg;application/ram;application/sdp;application/streamingmedia;application/vnd.apple.mpegurl;application/vnd.ms-asf;application/vnd.rn-realmedia;application/vnd.rn-realmedia-vbr;application/x-extension-m4a;application/x-extension-mp4;application/x-flac;application/x-flash-video;application/x-matroska;application/x-ogg;application/x-streamingmedia;audio/3gpp;audio/3gpp2;audio/aac;audio/ac3;audio/amr;audio/amr-wb;audio/basic;audio/dv;audio/eac3;audio/flac;audio/m4a;audio/midi;audio/mp1;audio/mp2;audio/mp3;audio/mp4;audio/mpeg;audio/mpegurl;audio/mpg;audio/ogg;audio/opus;audio/scpls;audio/vnd.dolby.heaac.1;audio/vnd.dolby.heaac.2;audio/vnd.dolby.mlp;audio/vnd.dts;audio/vnd.dts.hd;audio/vnd.rn-realaudio;audio/wav;audio/webm;audio/x-aac;audio/x-aiff;audio/x-ape;audio/x-flac;audio/x-gsm;audio/x-it;audio/x-m4a;audio/x-matroska;audio/x-mod;audio/x-mp1;audio/x-mp2;audio/x-mp3;audio/x-mpeg;audio/x-mpegurl;audio/x-mpg;audio/x-ms-asf;audio/x-ms-wma;audio/x-musepack;audio/x-pn-aiff;audio/x-pn-au;audio/x-pn-realaudio;audio/x-pn-wav;audio/x-real-audio;audio/x-realaudio;audio/x-s3m;audio/x-scpls;audio/x-shorten;audio/x-speex;audio/x-tta;audio/x-vorbis;audio/x-vorbis+ogg;audio/x-wav;audio/x-wavpack;audio/x-xm;video/3gp;video/3gpp;video/3gpp2;video/divx;video/dv;video/fli;video/flv;video/mp2t;video/mp4;video/mp4v-es;video/mpeg;video/mpeg-system;video/msvideo;video/ogg;video/quicktime;video/vnd.mpegurl;video/vnd.rn-realvideo;video/webm;video/x-avi;video/x-flc;video/x-fli;video/x-flv;video/x-m4v;video/x-matroska;video/x-mpeg;video/x-mpeg-system;video/x-mpeg2;video/x-ms-asf;video/x-ms-wm;video/x-ms-wmv;video/x-ms-wmx;video/x-msvideo;video/x-nsv;video/x-ogm+ogg;video/x-theora;video/x-theora+ogg;x-content/audio-cdda;x-content/audio-player;x-content/video-dvd;x-scheme-handler/mms;x-scheme-handler/mmsh;x-scheme-handler/rtmp;x-scheme-handler/rtp;x-scheme-handler/rtsp;
X-KDE-Protocols=ftp,http,https,mms,rtmp,rtsp,sftp,smb
Actions=new-window;

[Desktop Action new-window]
Name=New Window
Exec=gnome-mpv --new-window

Note the 'Icon=io.github.GnomeMpv' stanza. Thunar does not show this icon by default.

In fact, several GNOME apps desktop files use a similar naming pattern, which, as far as I can determine, is a valid naming scheme according to https://standards.freedesktop.org/desktop-entry-spec/latest/.