when i make transaction i also access with seed,i am 100% sure about this,i cant explain
bob123 is correct... you should NEVER need to use your seed... you should plug in the nano, enter your PIN only... then it should be ready to be used.
The only time you ever need to re-enter the seed is if you wipe the device (ie. you enter the wrong PIN 3 times)... or you have to buy a new device because your old one got lost/stolen/destroyed.