genisoimage is a very old version of mkisofs (from September 2004) with plenty of Debian specific bugs added.
genisoimage doesn't support large files correctly. The people behind genisoimage just removed a warning message.

Platforms that come with genisoimage usually don't include the real mkisofs, so if you like to use mkisofs, you
will first need to download/compile/install the real tools from:

ftp://ftp.berlios.de/pub/cdrecord/alpha/

Note that you need to specify -iso-level 3 or greater to enable large files.

Also note that if you are interested in mounting large files from UDF and use the -sort option (-sort is used by knoppix)
you will need to use the latest cdrtools (at least 3.01a12) to get readable UDF files.

BTW: if you like to write BD-R or BD-RE disks, you need the official cdrtools anyway.