In two MR3020 same problem: it does not install piratebox

Hoping to be clear enough, despite my floundering english...

I installed and runned succesfully my first PirateBox some weeks ago. Now I wanted to make new boxes.

I got some new MR3020, discovering they are a polish version! Any way I did not believe this was an issue and proceeded with the installation of PirateBox, finding myself in this situation:

telnet 192.168.1.1 - > OK
changed password -> OK
ssh root@192.168.1.1 -> OK

But... no trace of PirateBox, just the OpenWrt running.

I found that usb was not mounted; so no install.log, nothing. I could mount it by hand:

mount /dev/sda1 /mnt

... finding just the install folder, that I haved copied from a fresh unzip of install_piratebox.zip before.

The OpenWrt image was the same I have been using in the first successful installation:

openwrt-ar71xx-generic-tl-mr3020-v1-squashfs-factory.bin

I've tried also to put this image on the usb pen and then trying to reflash with

mtd write -r openwrt-ar71xx-generic-tl-mr3020-v1-squashfs-factory.bin firmware

but the result was the same.

I tried everything again on an another MR3020 obtaining the same results...

Really grateful if someone could give me a hint...