Drag selecting in the 2d view ports seems to always include some of the actors in the level whether they are in the selection range or not. Even selecting on blank space these actors (they seem to be all blueprint actors too) end up being selected.
Here’s a video - YouTube
Almost never used the 2D views so this is new to me. Happens in 4.8.3 and 4.7.6 (on two different projects). Doesn’t seem to happen in any of the example projects though.