Why do you restore and sometimes not
How is it that sometimes you take the iPod apart and put ot together again, you have to restore and other times you do not?
"I have ""my"" theory about those problems (it happens on other devices too)
when you think about computer hardware changes, something like replacing ram, graphic cards and other stuff - everybody tells you - unplug it - remove the power cord from the computer - even if it's not powered on - remove the cable!
thats because of the virtual power button - it only virtual - not a regular switch like a light switch, only virtual and always powered.
the iPod (and the iPhones too) also have only vortual switches - they are programmed to wait for a special button is pressed to wake up (an iPod is only ""switched off"" when the battery is empty).
for example - think about a watchdog, he waits until some stranger came by and wants to get inside, in that moment he will went berzerk and do what he is trained for.
now let's get back to the beloved gadget - the programmed watchdog is always powered on and waits until someone presses the select button, in that moment he does what he's programmed for, he starts the system and you can use the device. this function needs a powered and running system in the background.
now to your actual problem - if you start digging in the system, replacing parts, disconnecting powered parts - the software simply crashes sometimes, if a cable or connector isn't connected 100% perfect, it could led to a little short - this short can be enough to destroy internal parts or as i already said - crash the software.
i hope that i explained it understandable"