I have two builds of Arma installed:
Stable branch through normal steam installation
Dev branch installed by Arma 3 Tools Game Updater.
OBS:
If Game Updater has not run during the current Steam session, the Dev branch Arma Launcher displays a useful DEV banner in the top left corner.
However, if the Dev branch has been updated by running the Arma 3 Tools Game Updater, the DEV banner does not display in the launcher. This behaviour persists until Steam is restarted.
EXP:
The dev branch Arma Launcher should always display the DEV banner. The stable branch Arma Launcher should never display the DEV banner.