I just want to add my voice to the throng of people affected by junk turrets falling through surfaces in POIs. For me its happened with almost every kind of tile that isn't ground. It has happened with full-size concrete such as the ones making up a porch of an apartment tower or the "lip" off a roof that extends outward a space further than the building below it. Sometimes I can dig them out from under the lowest non-ground surface of the POI and sometimes their gone forever. This is really annoying when its a L6 turret since, if the Turrets Syndrome skill descriptions are accurate, you c