Packages included in build seem to change arbitrarily

I have been building snapshots for my BPI-R64 and ran into a really odd issue where the packages that are baked into the image seems to change. Specifically the "mkf2fs" package. For example:

  1. Build snapshot with the released .config unchanged, sysupgrade is successful and the upper filesystem is formatted with mkfs.f2fs giving me a proper overlay.
  2. I then add LUCI and a couple wifi cards as baked-in packages (nothing removed), but then on sysupgrade it fails to format the /overlay partition with a mkfs.f2fs not found error and reverts to ramdisk only.
  3. I change Utilities->Filesystem->mkf2fs from a module to built-in and rebuild the snapshot, sysupgrade is successful again.

I understand why the overlay fails to get formatted in #2. I can't understand how it succeeds in #1. The provided .config has it set as a module, so it shouldn't be in #1's image any more than it was in #2's image.