Comment 5 for bug 1443692

I have exactly the same problem on Kubuntu 15.10.

Installer stopped, when format the root-partition.
Installer run "mkfs.ext4 /dev/sdaX". When i run this command manually, it ask my to press 'j' ("Ja", German for yes).
I send this Key to the process. After that Installer continue.

kubuntu@kubuntu:~$ ps -Alf
[...]
0 S root 31995 31975 0 80 0 - 1614 poll_s 11:37 ? 00:00:00 log-output -t partman --pass-stdout mkfs.ext4 /dev/sda7
0 S root 31996 31995 0 80 0 - 5492 pipe_w 11:37 ? 00:00:00 mkfs.ext4 /dev/sda7
[...]

kubuntu@kubuntu:~$ sudo mkfs.ext4 /dev/sda7
mke2fs 1.42.12 (29-Aug-2014)
/dev/sda7 hat ein ext4-Dateisystem
        zuletzt auf / auf Sat Oct 3 13:47:59 2015
 eingehängtTrotzdem fortfahren? (j,n)
[CTRL+C]

kubuntu@kubuntu:~$ sudo bash
root@kubuntu:~# echo "j" > /proc/31996/fd/0