The keybindings.txt file copies just fine and my keybindings copy over, but the options.txt file, despite being saved with the correct settings, does not, leaving all GUI settings default.

Forge: 2768
DefaultOptions: 9.2.8

Here's the file it saved in the defaultoptions folder that isn't working:
options.txt

If you are using FoamFix Anarchy Version, disable B:initOptions in the FoamFix config or else Default Options will not work. See #25 for more info.

What is going on here? I got 3 emails for this but only one post is showing up.

To answer them:
I do have vanillafix installed, but I don't see how that's related since it's essentially a debug assist tool.
I do have foamfix installed, but not the anarchy version (said version conflicts with other mods in my pack anyway). Reading through that thread, it seems like the issue prevents default options from working at all, what I have is a partial failure (default options can write to options.txt as expected, but only copies over keybindings, and the rest generates as default).

As for the lack of comment, I can only surmise that most people don't use the function to save volume settings and other stuff very much.

Please post your mod list and a log from Minecraft starting up, some mod is probably generating an options file before Default Options can do anything. The reason keybinds are working fine is that they are handled differently (and stored in a different file).

What kind of options.txt is being generated when Minecraft starts up? That could give hints as to which mod is generating it.

Mods list: https://minecraft.curseforge.com/projects/continuity/relations/dependencies + Galcticraft (this is the best way I have to list things, sorry if it's not very great).

Here's a log, startup to main menu then exit:
latest.log

And a debug log in case it's useful:
debug.log

as for what kind of options file is being generated, I'm not sure what precisely you mean. I'll attach my current one, as it's probably faster:
options.txt

Finally found out what's going on here, after working on squishing ram usage some more. Foamfix anarchy and lawful got merged, and the option mentioned is in the new version simply called foamfix, and is true by default.

Suggested resolution: update the warning on curseforge to reflect this, and make a note of it for future reference.