As default, the arma 3 (and 2) the space makes you select all of your units, but for no reason at all that i could find in controls, when i press space it immediately tells everyone to dismount.
Why on earth would somebody think that this is a great idea? I just want to have the Arma 2 unit control scheme, i actually tried it but for some reason "select all units" is §. When i changed it to the space bar, the problem remained.
I checked all the controls i could find, and i did not find anything that would cause the game to do this.