I can now reproduce the restore problem.
I had MC 15.0.96 installed on an old PC (which has been rarely used). I created a new library backup file and installed the build 167. At this stage the library files were present and the old options were as before.
Then I created another new library backup file, copied all library backup files to a safe location and did a full uninstall (= removed the registry and library files).
I reinstalled the build 167 and restored the "build 96" backup file. The library was restored, but not the settings. Then I tried the "build 167" backup file with the same results.
Then I installed the build 163, but that didn't change the behavior.
Finally I installed the build 159. It can restore the library data and the settings from the "build 96" backup file correctly. Also the "build 167" backup seems to restore at first, but after the recommended restart the library shows up as empty.
Apparently also the "build 96" backup file does not restore correctly anymore. After a restart the library is always empty.
Next I am going uninstall once more and try a clean install of the build 159...
EDIT
The OS is XP and the Windows user account has admin rights. No error messages.