There is now a warning that it might take a while for the process to find if there are more than 20 directories/files found (based on if you have searching for subdirectories turned on or off). Additionally there's also a minor logic fix in this commit.
Having the 'One output file per extension' checkbox unchecked now merges all files into a file called merged_files.txt, rather than having the filename of the last extension it would merge.