When human runs out of ammo for primary weapon, he can't toggle inventory items (throw grenades, use medkit, change weapon, toggle jetpack) sometimes. These actions are conditioned on (game/bg_pmove.c line 2712):
pm->ps->weaponTime <= 0 || pm->ps->weaponstate != WEAPON_FIRING

pm->ps->weaponstate is never cleared since it is set to WEAPON_FIRING and pm->ps->weaponTime is repeatedly set to 200ms in out-of-ammo block of code in PM_Weapon() causing the glitch until weapon is changed.