The download_cache removal code turns out not to be working again (or: still)
Older bug report including fix here.
The file selection works fine now, but the xargs rm -f does not.
Since the code is not entering the download_cache directory first, it’s trying to remove those files somewhere else.
So I guess it should be something like
ls -tr #{CACHE_DIR} | head -n -#{CACHE_MAXIMUM_SIZE} | awk '$0="#{CACHE_DIR}/"$0'| xargs rm -f
