If using an ancient live USB to create a new one with Tazpanel, Tazpanel keeps the existing /home/tux directory (as Tazinst does), that can give unexpected comportments.
In my case I recycled a live USB RC4 (I believe) to do a live USB 4.0 -> no logout icon in the right top corner, a grey task bar in the bottom of the screen and nothing inside, necessity to use [Alt]+[Tab] to access to open applications, battery monitor freezed...
So, erase /home/tux or format the key before.
(I didn't check using gen-liveusb and gen-iso2usb in command line but I suppose it is the same)