Edit ubb_lib_files.cgi and hunt for the instance of '$maxmemfields' with the number 36 after it. Change 36 to 100 so that the re-build process recognises the extra 'hack' related fields.
Note there's a second instance of $maxmemfields with 36 after it, change that to 100 as well, although I don't think the code for the second instance is working yet (test code).