It only seems to loosely follow T1E, in that the interpretation you're using is far more nebulous. T1E suggests that preps be made apparent from the start, as in it should be made known that they are primarily focusing on [b]that thing[/b] beforehand, not an off the cuff 'sudden' spike in focus when it's convenient. If that's the case this rule should still apply to me, provided I suddenly decide to place all of my characters focus on something randomly. 

Edit: Provided I decide to go along with this intepretation, it would still be subject to the one prep a turn logic. If you created a rune in this post, but were charging something else in that post, then  when you let that rune off later it could not logically count as a matured prep, since you were already prepping your one action in the post that the rune in question originated in. To do otherwise would violate the 'one thing prepped a turn' logic, because this would suggest you charged two things at once.