[wiko-lenny3] osk-sdl causes reboot

I'm trying to run osk-sdl, but I only get this output before the phone reboots:

/ # osk-sdl -n root -d "$partition" -c /etc/osk.conf -v
commandline read: osk-sdl
commandline read: -n
commandline read: root
commandline read: -d
commandline read: /dev/mapper/mmcblk0p20p2
commandline read: -c
commandline read: /etc/osk.conf
commandline read: -v
(*) Direct/Thread: Started 'SigHandler' (889) [CRITICAL - OTHER/0] <85316>...

   ~~~~~~~~~~~~~~~~~~~~~~~~~| DirectFB 1.7.7 |~~~~~~~~~~~~~~~~~~~~~~~~~~
        (c) 2012-2015  DirectFB integrated media GmbH
        (c) 2001-2015  The world wide DirectFB Open Source Community
        (c) 2000-2004  Convergence (integrated media) GmbH
      ----------------------------------------------------------------

(*) DirectFB/Core: Single Application Core. (2017-10-03 12:19)
(*) Direct/Memcpy: Using libc memcpy()
(*) Direct/Thread: Started 'Fusion Dispatch' (890) [MESSAGING - OTHER/0] <85316>...
(*) Direct/Thread: Started 'VT Switcher' (893) [CRITICAL - OTHER/0] <85316>...
(*) Direct/Thread: Started 'VT Flusher' (894) [DEFAULT - OTHER/0] <85316>...
(*) DirectFB/FBDev: Found 'mtkfb' (ID 0) with frame buffer at 0xbf300000, 11040k (MMIO 0x00000000, 0k)
(*) Direct/Modules: suppress module 'linux_input'
(*) Direct/Thread: Started 'Keyboard Input' (895) [INPUT - OTHER/0] <85316>...
(*) DirectFB/Input: Keyboard 0.9 (directfb.org)
Connection closed by foreign host.

any idea?