CKAN user here.
I compared files inside the v2.4.3.1 archive CKAN downloads to it's cache and files CKAN displays as content of entry for TweakScale - and I see only files inside the "Extra" folder are displayed!
If I delete the "Extra" folder, CKAN will then display all the files inside GameData folder and successfuly installs them too, making TweakScale v2.4.3.1 working. (it installs from cache, so it installs from the archive I deleted the "Extra" folder from)
So at 99% it's the "Extra" folder which somehow makes CKAN to fail.