[Tails-dev] TAILS USB clone and install issue.

I don't know why from TAILS 1.4 there are some trouble to clone TAILS to
a new USB stick.

Sometime it works, sometime it don't work.

I try to clear MBR and full disk by
dd if=/dev/zero of=/dev/sdb

I try to read the MBR and EFI partition table via hex heditor and reset
manually the bytes.
But anyway with some USB stick don't finalize the TAILS clone operation.

Anyway, if i copy TAILS by dd command, the copy works fine.

All usb key are tested and verified.

Is there a bug in TAILS clone and install application or i must use dd ?