When teleporting in creative mode, I teleported to a place I had already build quite a bit in. A large portion, but possibly not a whole chunk, of normal terrain spawned amid what I had already built and created.
Environment
macOS High Sierra (10.13.4)
MacBook Pro (Retina, 15", Mid 2014), 2.8 GHz Intel Core i7, Intel Iris Pro 1536 MB
Java 8 Update 171
No, this isn't resolved. My harddrive has a confirmed over 300GB free and it is only several years old (solid state). This ONLY occurred once I tried using Minecraft 1.13-pre1, so therein is your error. If you think you fixed this some time ago, then you're very wrong. I see that others who had this error also did not necessarily suffer from a full and or faulty harddrive. Do you want feedback on 1.13-pre1 or not?