Muramana and it's toggle

i have played more than 6 games trying a new build with Muramana and it's toggle and during those 6 games for the life of me i could not figure out whats wrong? why am i not doing more damage? after playing some practice games with bots i come to find out that Muramana does (correction does not)come with its toggle turned on! i mean it kind of defeats the purpose for getting that item of the toggle is not automatically turned on! why else would i choose to build Muramana if i did not want to use its toggle which converts 3% of current Mana to deal bonus physical damage equal to twice the amount of Mana consumed?