I've only just experienced the same issue in my current project. Using SketchUp 2014 Pro, exporting as a 2D graphic into AutoCad 2011.
I started working through the 9 rooms in my project, first some rooms with just a straight run of cabinets, which imported perfectly from SU into AutoCad. Then, I got to this printer room and although it displays the scene perfectly in SU before exporting, in AutoCad it shows the graphic complete with all hidden line geometry... what's up with that?!
![Correct elevation in SU, done in a "HiddenLine" style scene](/uploads/imported_attachments/1jP2_Capture1.JPG "Correct elevation in SU, done in a "HiddenLine" style scene")
Have started hiding geometry, one-by-one, to see if it's a "Buoy box" effect like you're finsing. Also attempted saving original SU file as a 2013, and also in SU 8, but didn't change the outcome in AutoCad.