[nhedgehog]

No I didn't. What I just did in pbterm was:
1) NotJailbreaked device
working:
ls /mnt/secure
cp /mnt/secure/device.cfg /mnt/ext1/
not working
ls /mnt/secure >> /mnt/secure/test.tst

2) Jailbreaked device
working:
ls /mnt/secure
cp /mnt/secure/device.cfg /mnt/ext1/
not working
ls /mnt/secure >> /mnt/secure/test.tst
/mnt/secure/su ls /mnt/secure >> /mnt/secure/test.tst

PS: Funfact device.cfg & device.cfg.back are existing in /mnt/secure
device.cfg has have_opds=1 in it, so your installer worked despite my previous comment BUT library does not show the Network library entry. Sorry I didn't check the device.cfg itself previously.