It's not the purge.... It's due to the ecm having to relearn and back calculate everything from temp parameters. If you notice when you do a restart, your intake valve temp restarts somewhere right around coolant temp then immediately starts counting back up. I imagine all temp parameters are doing the same thing - injector, intake and so on until the 10 to 15 minute idle period has passed. I also noticed that it typically waits and "fine tunes" it's own calculations until after you have atleast free revved it a little or ran it through the gears once, then it will settle in one place. At that time you can ussually reset your fuel trims and start your datalogging. I also can not emphasize enough on the importance of allowing it to go through atleast 1 or 2 cold start to operating temp idles sitting still without load after final programming. Will save on any unforseen restart issues durring temp cycles down the road...
All programmers (Including OE, SCT, Diablo & HP that I can confirm) have this issue... It's just a relearn that it unfortunately has to go through. AND as previously stated, the closer the tune gets, the less time it seems to take. The worst I've had it was 15 minutes, so I try to let it idle that long, run it through the gears, come back to stop then start datalogging. I've also noticed it's way worse in VE setup vs combined. If it's a starter tune, I datalog in open loop as it's not as temp calculation sensitive right from restart, then durring closed loop tuning use the wait period if that would help anyone...
NOW with all that being said I did just have one really kick my butt where 3" aftermarket non heat shielded exhaust was installed on a corvette and while on the dyno after about mid morning it would start boiling or super heating the gas in the tank causing the purge to pull in excess vapors throwing things off. Was able to get a fan blowing across under the tanks to cure that. Never the less it also got exhaust wrap and tank insulation afterwords... BUT this is the only time purge has been an issue.