Mantra resets every time you enter the water (and the ones you charged up in water resets if you come on land). It also resets when you zone in (like say, zoning into PvP), as well as when there is any “world event”, like the PvP gate opening…or even when the announcer says “point X is taken”. At least that happened to me last game (which is coincidentally my first and only PvP match so far).
I think this kind of breaks the build entirely, seeing as at least the port map that I was PvPing in forces you to cross the water, or walk all the way around the edge.