Comment # 3 on bug 1200077 from Fabian Vogt

(In reply to Ulrich Windl from comment #2)
> I could boot the same stick on an older PC using an Intel CPU (6th gen).
> However I noticed that not just the usual two boot entries (UEFI and legacy)
> were displayed, but several legacy ones. That might be a bug in the PC's
> BIOS, or maybe that's the issue that prevented boot on the Lenovo TP.

It's possible that it can't decide whether to boot it as EFI, or legacy in USB,
HDD or CDROM emulation mode... Do you have something like a "Boot from EFI
file" option you can try?

> I also noticed that during first boot a third partition was created on the
> USB stick, adding an ext4 filesystem used as overlay filesystem.
> Usual expectation of a live system is that it does not change the medium it
> is booted from, at least not without asking for permission to do so, but
> that might be a different issue.

That's expected, that's the automatic persistence feature.