Hm... On a fresh 2.10 placing this USB_Installl.desktop into /home/tc/Desktop it works as expected:
[Desktop Entry]
Version=1.0
Encoding=UTF-8
Type=Application
Name=USB Installer
Categories=Application;
Exec=sudo usbinstall
Icon=dialog-warning
Terminal=true
StartupNotify=false
but doesn't work in /usr/local/share/applications I do not know why it behaves differently. When usbinstall terminates with an error message terminal window is closed immediately
1. Not really helpful to only work in home.
2. Should work in either /usr/share/applications or /usr/local/share/applications.
As I said, LXDE does and is the most compliant. XFCE less so, Englightenment, I am waiting.
The .desktop items are not that difficult. I am looking consistency in support of a standard, otherwise much effort will not result in good experience.