auto switching !!

hey

i got this problem from over a week but i wanted to make sure its a real problem , so here is it :

today when i was playing compound snipers only , i jumped to hit some 1 by awm , i found that it auto switched to knife , so i died like a chicken , & this problem happened with me like over 20 times today

so can u fix it coz i don't like to find myself die from a nob coz this stupid bug