I don't claim to be a KiCAD "expert", and I'm certainly not a developer, but I have gleaned most of the following information from this Forum over the last two years or so.
Sometimes KiCAD is a little sensitive about selecting things with a click (or with the hotkeys "E", "M", "R", etc). Zooming in to a high magnification helps, but I usually do a "Block Select" by "drawing" a box around the item I want to edit, then doing a right-click.
Expect to see this kind of inconsistency among the menus, documentation, and file syntax. KiCAD is an open-source collaborative effort of many people, from several cultures, with several different first-languages. Some of the terms and phrases that seem strange or confusing in English are quite reasonable when traced back to the native language of the original developer.
It's impressive that you used a text editor to examine the KiCAD file. ("Notepad++" has a lot of fans on this Forum!) All of KiCAD's data files are plain-text, human-readable. On several occasions I have clarified my understanding of something in KiCAD by opening the data file and studying its syntax. It's even possible to edit your board or schematic in a text editor, but I wouldn't recommend doing so unless you have exhausted all other approaches.
I believe the DXF version officially supported by KiCAD is rather old - perhaps version R12, circa 2005. A few Forum members seem to be knowledgeable about incompatibilities with other versions. KiCAD support for EXPORTING a DXF file seems to be very crude and incomplete. There are 3rd-party scripts that do a much better job than the built-in feature.
Here's a filled circle with 100 mil diameter, using this method.
It's rumored that this problem comes from a buggy, "cracked" version of Gerber software. I haven't had this problem yet, but I'm sure the day will come when I do. A suggested accommodation is to create the circle from two arcs:
The two vaguely obscene shapes on the left are 180 degree arcs, offset by 35 mils for illustration purposes. When their center points are aligned you get the filled circle shown on the right.
The Analog Artisan within me likes my circles to be a single-entity circle, not a collection of a few dozen line segments.