As I reported earlier this happened to my unit as well. I contacted support, and they had me send the unit in for battery replacement. They returned a new unit. I tried it, and the new one does the same thing, only this one does it (so far) every time. I've played with it a little and found some more.
If I turn the brightness down one unit (at least I think it's one, in the iFly there's no indicator), the unit goes to the countdown upon power removal. However, when the unit is restarted, the screen seems to be reset to 100%. So to use this work around I'll have to remember to turn the intensity down each time I turn it on.
If I turn the iFly on via the button without plugging in the external power, it starts up in a reduced intensity, and brightens up a bit once the power is plugged in, however if power is removed it shuts down immediately.
If I exit the application, leave iFly running in the background, go to screen brightness settings and turn it down a notch, retun to iFly, the screen stays darker, if I then unplug it starts the countdown. This setting remains IF I have the unit restart to 'Windows". Once I run iFly it resets to 100%.
I tested these a couple of different ways, but it seems that when iFly starts up it resets the "Windows" screen settings to 100%, and the Automatic Night Mode off.
So, with all that I have some suggestions.
While I'd like to be able to use my 740 at full brightness and not have it shut down immediately, I'd like to, as a workaround until this issue is resolved, be able to reduce the brightness by one or two notches and have it persist whenever iFly starts.
Change the programming in the iFly so that it doesn't change the "Windows" Brightness settings. I'd like to use the automatic night mode found there, as well as the regular brightness mode.
Develop programming so that if power is removed, the screen brightness automatically dims enough that the unit doesn't immediately shut down.