The duration of the animation of switch to the launcher approximately 4 seconds. Theis time the player's character will not be able to sit down and will be the perfect target for enemy. As we know in Arma, four seconds is enough to get a lethal bullet between the eyes.
And only after switching animation, the player character will respond to the Crouch command, and will be crouched. Sometimes, this feature very annoying to the player during combat. For this reason, the player character can be killed, because this impotence prevents to control the player's character effectively.
Please Note! For comparison, if the player will change his weapon at the full erect position, then this bug does not occur! The problem will occur only if the player has started the change of weapon from a prone position.
@BIS, Please fix this, this should work also well as when changing the weapon from a standing position