How can i stop the 2 strings slipping?

i own a schecter c-1 fr and i this week restrung it so i am going through the usual spring and string tension stuff so it stays in tune but as i play the B and E strings keep slipping out of tune but the rest are fine. i don't want to tighten or loosen the springs because i dont want the others to go out of tune so what can i do?