Going prone in craters can allow you to get under the map.
I have noticed this bug only in Fallen Heroes - on Far German side over looking the road where the Allies cross to get into the park.. There is a crater which if you go prone in or against its wall you will start to sink through it and can view the under world...
I am not sure if you can fall all the way into it but I do know you can "swim/jump" out of it... I was having a good game and did not want to ruin it by finding out.