Pressing "Toggle raise weapon" with a sidearm equipped while upright causes the player to lower his weapon. But pressing "Move Forward" causes the player to raise his pistol, rifle don't raise.
Pressing "Move Forward" With "Combat Pace" and or "Walk or run" - pistol don't raise.

Switch to your sidearm and press the key "Stand Up (Toggle)", your character will lower his weapon for no apparent reason.

Arma 2 OA with COSLX mod has a similar bug - press the key "Stand Up (Toggle)" your character hides pistol.