I filed a Gentoo bug, but was told that this is an upstream issue. See

http://bugs.gentoo.org/show_bug.cgi?id=347802

for the details. Here is the message I get when emerging xfburn-0.4.3-r1 (Gentoo version number):

 * /usr/share/applications/xfburn.desktop: value "application/x-cd-image" for
string list key "MimeType" in group "Desktop Entry" does not have a semicolon
(';') as trailing character -- (will be fatal in the future): value "Archiving"
in key "Categories" in group "Desktop Entry" requires another category to be
present among the following categories: Utility

And here is the file /usr/share/applications/xfburn.desktop (which I never
changed):

[Desktop Entry]
Version=1.0
Type=Application
Name=Xfburn
Name[en_GB]=Xfburn
Comment=CD and DVD burning application
Comment[en_GB]=CD and DVD burning application
Exec=xfburn
TryExec=xfburn
Icon=media-cdrom
MimeType=application/x-cd-image
Terminal=false
Categories=X-XFCE;GTK;DiscBurning;Archiving;AudioVideo;
StartupNotify=true

Actions=BurnImage;

[Desktop Action BurnImage]
MimeType=application/x-cd-image
Icon=media-cdrom
Exec=xfburn -i %f
Name=Burn Image (xfburn)
Name[en_GB]=Burn Image (xfburn)

Not sure it's something I have to worry about.