The Psychic Power 'Strength of my Enemy' allows you to enhance any (natural) weapon you have to deal one point of strength damage with each succesful hit. This drained strength is then added to your own as an enhancement bonus.
The power itself clearly states that it lasts for 1 round per lvl. However, the effect of this power is NOT "you get a strength bonus". The effect of this power is "As long as the effect last, you can drain strength from your enemies." So how long does the strength bonus last? Indefinitely? Until the effect ends? Or "1 round/lvl from the moment you drained this specific strength point?" Or, to keep bookkeeping easy: "1 round/level from the moment you drained the last point from a specific creature", since each creature's drained strength is counted as a seperate bonus.