Yes, there seems to be something wrong with the docomatic documenting private fields, like FDx1.
I guess this is because they are declared "strict private" and not "private" and probably docomatic doesn't understand it. As said, it is in my todo list to someday move from docomatic to document insight. But last time I tried document insight it crashed with FlexCel code, so I am giving it time to improve.
I personally just ctrl-click the FlexCel object (you need to do it twice, because the fist ctrl-click goes to a proxy unit). All documentation in the chm is from the xml docs in the code, so you can read the code directly (if you skip over the <xml> tags). Of course, for this to work you need to setup the browse path correctly. The installer does it, but if you have another build system, you should see that the browse path points to the FlexCel folders.