Madness is often associated in the play with not behaving 'properly'.

Malvolio asks the revellers, Have you no wit,   nor honesty but to   like tinkers at this time of night? (II.3.75–7).

Ask yourself: To what extent do you feel that Shakespeare wants us to believe that Olivia would object to this mad behaviour? Or do you feel this is more to do with Malvolio's wish for sobriety?