This bug is still present when creating bootable USB from Ubuntu 15.04 Vivid Vervet release ISO with Ubuntu 14.04.2 LTS Trusty Tahr's usb-creator-gtk.
(the workaround "cp /usr/lib/syslinux/gfxboot.c32 /path/to/usb-media/syslinux/" works though)
This bug is still present when creating bootable USB from Ubuntu 15.04 Vivid Vervet release ISO with Ubuntu 14.04.2 LTS Trusty Tahr's usb-creator-gtk.
(the workaround "cp /usr/lib/ syslinux/ gfxboot. c32 /path/to/ usb-media/ syslinux/ " works though)