This teaser is based on a weird but true story from a few years ago.

A complaint was received by the president of a major car company:

"This is the fourth time I have written you, and I don't blame you for not answering me because I must sound crazy, but it is a
fact that we have a tradition in our family of having ice cream for dessert after dinner each night. Every night after we've eaten, the family votes on which flavor of ice cream we should have and I drive down to the store to get it. I recently purchased a new Pantsmobile from your company and since then my trips to the store have created a problem. You see, every time I buy vanilla ice cream my car won't
start. If I get any other kind of ice cream the car starts just fine. I want you to know I'm serious about this question, no matter
how silly it sounds: 'What is there about a Pantsmobile that makes it not start when I get vanilla ice cream, and easy to start whenever I get any other kind?'"

The Pantsmobile company President was understandably skeptical about the letter, but he sent an engineer to check it out anyway. He had arranged to meet the man just after dinner time, so the two hopped into the car and drove to the grocery store. The man bought vanilla ice cream that night and, sure enough, after they came back to the car it wouldn't start for several minutes.

The engineer returned for three more nights. The first night, the man got chocolate. The car started right away. The second night, he got strawberry and again the car started right up. The third night he bought vanilla and the car failed to start.

There was a logical reason why the man's car wouldn't start when he bought vanilla ice cream. What was it?

(The hint may prove helpful)