The code for UNIX shortcut handling has several minor issues:
PNG files are broken after copying to the user's pixmaps directory.
User shortcuts on the desktop are duplicated for each call, because they get added a timestamp to the filename each time. This results in adding one and the same shortcut again to the desktop for each installer execution.
There is unused code and code which can be replaced by using utility methods of the Apache commons-io library which is part of each installer in IzPack 5.
Automatic code inspection of com.izforge.izpack.util.os.Unix_Shortcut complains about potential bugs (NPEs and more) and incomplete comments.