Lead time based ATP does not work when user defined lead time is zero days

Summary:

We are using lead time based ATP with lead time as user defined and user defined lead time days = 0 but when we do GOP inquiry we get ship date as infinite time fence and not request date + 0 days. But if we use user defined lead time days = 1 then the rule works as expected and returns ship date of request date +1 day and also the promising mode shows as lead time promising as opposed to infinite availability when we check pegging properties in the GOP pegging tree.

Is user defined lead time of 0 days not allowed when atp is lead time based?