
The gist of it is that when you cast it and enter the temporal form, the bonus temporal damage you get from your highest damage type isn't reactive to that damage type when you swap gear.
So, my corrupter there had ~200% bonus blight damage (After buffs such as lifetap, and that sustain that procs bonus blight damage on crit, etc), then cast Temporal Form. Now he has ~230% bonus temporal damage. Then spend a few of it's 10 turns swapping into other gear, for instance I swapped my staff for Corpathus, my robe for a randart with 36 crit dmg, and a crit dmg pickaxe. Lost like 70 blight damage from those 3 swaps, and my 5 turn debuff that gave me +39 can run out, but my temporal damage is unaffected, and I gained over a 100% bonus crit damage. You could concievably get it vastly higher if you carried around all the good temporal gear and/or had way more of it with swift hands, but I didn't realize this could be done till I was hanging around High Peak.
Anyway, it seems like there would be an easy fix of making your temporal damage while in the form change to always be set to your highest bonus type +30% instead of statically checked just that once.
As an aside, I wonder if there's interest in a discussion of general prodigy balance. I spent quite a time looking through/testing them on my last guy because I wasn't sure what to get, and am now of the firm opinion that this aspect of game balance is lagging quite behind the general class balance! Several prodigies are just so horrible that I can't imagine anyone using them who's trying to be effective, and quite a few more are just badly dominated by 2 or more that fulfill fundamentally the same role without offering any particular benefit. Could go through them and point out where I feel the biggest issues/offenders lie, and see if people agree.