Hi,
grml-live should contain the newest isolinux files in the template directory as the new syslinux (4.0) contains different 
modules.
Problem is that debian stable still has 3.x, so we would need to adjust grml2usb to work with different version (replace the 
files on the disk with the ones from the distribution for example)

For some details see http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=591635

Marking it as release stopper as the issue should be resolved before releasing a new version.

regards,
Ulrich