Applied Numerology doesn't feel right - rules question

I'm no less confused, because what Foote says means (to me anyway) that Applied Numerology's second effect does nothing. So I'm going to outline my thoughts on it here:

(the text in question is "Whenever you use a power in The Harpy's play area, you may increase by 1 or reduce by 1 one of the numberals in the text of that power.")

1. "Whenever you use a power" triggers normally appear to trigger after the effect of the power, for example Spite's "PL626 Compund Xi" which states "Whenever a hero uses a power, Spite deals that hero 2 Toxic damage..." and Benchmark's "Secondary Cannon" both work this way. Thusly, from experience, the effect is applied after the effect of whatever power you use (or so I believe anyway).
2. If it only changed the numeral for the power use that triggered it, it would say "You may first increase or decrease" (in my opinion) and would state that the effect went away at the end of the power use in some way, probably through phrasing it like "You may treat one numeral in the power as being 1 higher or 1 lower than it's printed value for the duration of that power". Hence, I believe it applies a continuous effect (like Heartbreakers damage increases)
3. If it does apply a continuous effect, like Heartbreaker, then how is the effect interrupted? In Heartbreakers case, removing him from play stops all the damage incresases as he'd re-enter as a new object. This implies that the increases are stored on him and disappear when he does. The question for Applied Numerology then is; Are the numeral changes stored on Applied Numerology (and thus end when it leaves play) or on the cards it changes (and thus ends when the modified card leaves play)

I feel like it shouldn't stack (for the purpose of easing the strain of carrying numbers around all game) but I can't be certain, so I seek a full clarification.

I feel like if it did that Powerhound it would be worded along the lines of "Whenever you would use a power in Harpy's play area, you may first increase by 1 or decrease by 1 one of the numerals in the text of that power for its duration.". As it is, it does not state that the increase or decrease afflicted on the numeral is undone at the end of the power's use nor does it state that the change is for this use of the power. Other cards that state "Whenever you use a power" apply their effects after the use of the power that triggers it rather than before, and that is the major problem I have. The power appears to modify numerals after you use the power, and not before.