You probably have an old version, or a version with an error, of the
.desktop file in
~/.local/share/applications. The "reading priority" of the launcher is:
- the local directory for desktop files in in
- the global directory for desktop files in
That means that if you start the application from the "right" (global)
.desktop file, the launcher will check for a local version of the
.desktop file on the next occasion and use the contents of that file.
You will have to remove the local
.desktop file, log out and in, and lock the icon to the launcher again.