Correct, the isolation switch should not need to be moved from AUTO
In fact and even alone for the following reasoning: if the isolations switch found to be unserviceable, this is a NO GO item! Check your MEL/MMEL/DDPG!
There is NO requirements to OPEN the isolation valve switch and this is indeed may be a requirement on pre-Classic variants like Jdscud said, but not required on the Classic and NG.
Think about HOW will you determine if the isolation valve switch functions properly in AUTO if you do not let it perform the function designed to be completed when selected in AUTO?
The ONLY time the switch should be moved from the AUTO into OPEN is when APU Cabin Air is used for air conditioning as the fuel flow for single pack operation on the APU is higher then for both packs by ~10%.
Of course, there is a NTO from Boeing to allow always opening the isolation switch valve to start... Is there a provision attached? Who knows... Someone must test the function of the isolation switch at some time prior to flight if it constitutes a No Go...