I get this occasionally trundling through the channel (western end of the channel- not the bit anywhere near Dover

) using the latest GWX incarnation with the 16km dobery. Watchman calles out 'Ship spotted!' but there's nothing in sight on a clear day, except a new map contact that appears about 50 miles away in an enemy port. About 15 minutes later after a dive to 60m at ahead slow, all of a sudden I get a cuple of destroyers buzzing me.
Don't know if I'm missing something and this is correct behaviour, but it seems a little strange to me; no a bug as such, just odd.
Anyone else see this kind of thing happening? Maybe the britishers are using a primitive SOSUS (or whatever the acronym is) in the channel in '39