Able to see the new shipment's promised date not "Multiple" after cancelling shipment totally ...

Hi eveyone.

In order to explain my question, I'd like to describe the test steps

1. Create Standard PO (1 Header - 1 Line - 1 Shipment - 1 Distribution)
2. Cancel the shipment and then create a new shipment with a promised date different from the cacelled shipment. The cancelled shipment is cancelled totally, ie. cancelled qty is the same as order qty.
3. We can see the "Multiple" in the promised date field of PO Line form.

My question is that,

From the user's point of view, they think of the cancelled shipment as deleted it.

So they were wondering why the promised date is "Multiple".