If an air unit with a withdraw date is rebuilt, it keeps that date. If the date is early enough it can arrive on map already overdue for withdraw.
This is my mistake, I just didn't think about it. And the withdraw date isn't shown in the unit info when looking at it from the rebuild unit screen. So if you aren't sure.... check before you rebuild by loading an earlier save, or checking in the editor.
example shown below just for fun.





" - BBfanboy