Underwater wrecks on radar???

[BigBadVuk]

I played yestrday and tonight again same quick mission:
ASUW intercept with Akula and SW...I went to PD slowly then i sreamed wire and rised ESm mast..as soon as i managed to get ping from esm and sonar tracker to same master I managed to sink both ships relativly fast(within 6-7mins)..So i droped contacts on nav map and i then i surfaced to enjoy the raide on state 5 sea...

So i retracted my floating wire..rised all my masts(exept periscope),started to ventilate and of course i rised radar mast..and then:bingo!!! some 4nm from me was surface contact!!!...1st time i was liek ups...crsh dive lower all masts...go under layer and pretend that im not here..but sonar didnt discovered nothing...when this happened again i realised that radar contact was very close to my last target so i then enabled Show truth and i realised that radar actualy picked dead ship on bottom of the ocean!..i know that wrecks can be shallow but WTH???If radar can detect underwater contacts then why do u need sonar?

So i asume that this is just a bug!..but very annoying 1 similar things happened also in OHP mission when u need to make to open sea from river(and some small attacking craft opposing u)

any 1 else had same problem?..as far as i can remember this was same on 1.00 and on 1.03 with or without LWAMI (preview version ) mod ..