Someone else' kill?

[Kafka]

Errr... glad to be back. I bet this topic has been addressed before. Often I find myself tracking a merchant, then all of a sudden I lose contact, and the merchant is sunk, and all I see is a grey icon on the map... Am I to assume that the merchant was sunk by another u-boat? Or is it just a bug? Can't be Axis aircraft or Navy doing the kill cause in my current game, it's still early September '39... playing now without RuB, btw. Couldn't find any earlier post talking about this, just yet. Danke!
K.

[Deep6]

Most likely bad weather and heavy seas did it in.

[Kalach]

Or a mine, you might want to leave that area very carefully ;)

[Von Scheerbach]

I had that happen off the west coast of Ireland one time. I set a couple waypoints to intercept and increased speed (and time compression). Next thing I know, it's a gray sunken ship icon. I just assumed another u-boat got it.