39 bombers tb by one submarine is this bug????

How is this posible i have 2 airtransport general , 11 inflantry and 39 bombers in marseille. but i move transports only ,my 39 bombers got tb with 1 submarine.sry i dont make ss.airtransport with 1 general and 11 inflantry moved to my capital to deffend but my 39 bombers got tb in marseille France




Val: i think that in some citys the tb still works with 1 unit
val: i got tb like 4 times in a row with a 100+stack
val:in africa near the cost there are a lot

(1/39)*100

2.56%

unlikely, but possible.