Hi all: I'm a complete rookie at this, but having fun. I found a couple of strange artefacts on my first 3D floor plan, link below. I assume I did something wrong, but can't find out what. The two grey triangles arrowed appear only at certain angles of inclination - any idea what they are please? Thanks.

https://drive.google.com/file/d/0B02yg_ ... RQS3c/view