DFU does not use iboot so it has more option like downgrading on certain idevices.
My bet is that after the restore you put back your old settings and did not setup as a new iphone.
A dfu restore installs a clean new ios version ALL info is wiped so there could be no re-occuring problem, however if you sync back to itunes you out back the old info an old problem.
If you are sure you haven't done that it is a hardware problem, if still under warranty you can exchange it with out limits.
If you did a dfu restore there will be no trace of the JB.
My bet is that after the restore you put back your old settings and did not setup as a new iphone.
A dfu restore installs a clean new ios version ALL info is wiped so there could be no re-occuring problem, however if you sync back to itunes you out back the old info an old problem.
If you are sure you haven't done that it is a hardware problem, if still under warranty you can exchange it with out limits.
If you did a dfu restore there will be no trace of the JB.