Very faint grid lines are visible in the water ponds in the mushroom forest.
http://steamcommunity.com/sharedfiles/filedetails/?id=592307772This secret safe inside Caerus Residential requires Perception to detect, but there is nothing inside it. It has been empty for me both times in two different DC playthroughs so I am guessing it's not a fluke. I haven't encountered any other detectable secrets in the game that were just there to troll me, so I assume this was not intentional.
http://steamcommunity.com/sharedfiles/filedetails/?id=603338510This medical locker inside Project Eos is a "ghost." It's semi-invisible and you can see the wall through it.
http://steamcommunity.com/sharedfiles/filedetails/?id=603911116There is a Box visible on these Shelves, but it is impossible to loot it because the Shelves get in the way of your pointer.
http://steamcommunity.com/sharedfiles/filedetails/?id=603911142This spot of the map in the Mutagen Tanks area behaves oddly. Look at the box where my character is standing--if you start to the north of it and click on the box, character will go directly south, passing right through the barrier and over the pit as if they were not there, instead of walking around to use the ramp as expected.
http://steamcommunity.com/sharedfiles/filedetails/?id=603911227"Forgetful" junk pile in DC:
http://steamcommunity.com/sharedfiles/filedetails/?id=605221580"Forgetful" vase in Tchortist camp; this one ate all the guns I was going to sell. How rude!
http://steamcommunity.com/sharedfiles/filedetails/?id=603338495Is it intentional or not that the... weird grub honeycomb things do not have a name? It's not possible to find the ones that contain oddities by pressing Tab, but maybe you meant for it to be that way, I can't tell.
http://steamcommunity.com/sharedfiles/filedetails/?id=605221610The Miner's Helmet is found next to the Miner's Corpse, instead of on it. It is a bit hard to see, and it would make more sense if it was looted through the corpse itself.
http://steamcommunity.com/sharedfiles/filedetails/?id=605221618If you blow up a wall in Caerus Residential with TNT, the nearby Faceless will investigate the noise. When I did this, they all eventually left, except the Doctor. He continues to stand an eternal vigil for that poor departed wall.
http://steamcommunity.com/sharedfiles/filedetails/?id=592307622