This is incorrect. When you execute a 1-white straight maneuver under the effects of Ion, you are instructed to remove ALL Ion tokens on your ship, regardless of how many there are.
I never realized this. This has only ever happened to me once, and I just assumed the guy I was playing with knew the rule so I didn't think twice about it. Thanks for clarifying!
I wish it worked like this, but I imagine that it was due to not gang banging ion tokens onto one ship in one turn and moving onto other targets while it slowly drifted towards the table edge for 4 turns.