I confirm this problem and there are at least 2 threads about this kernel power problem:
http://talk.maemo.org/showthread.php?t=71127
http://talk.maemo.org/showthread.php?t=72002

This is an age old problem.

I wonder if this is related, as always, to a too undervolted/overclocked/smartreflexed thingy...
Or also, battery patch with a too much downed idle profile

Just to be sure: It is not a problem of the phone restarting, it is a problem that the phone, when we try to restart, will give up at nokia logo and turn off.

KP46 is from far before battery/speed patch, so no.
Undervoltage, Overclocking and Smartreflex are easy to rule out, all is needed is to try on default, same thing happens since forever(at least in my case).

Also, I think that the voltages/clocks are set after the phone starts, which needs the phone to successfully start, which is the problem: The phone doesn't restart. It will give up at nokia logo, will turn off the screen and then the phone itself.

It does not happen with the stock kernel.

I tried:

"sudo reboot"

"root
reboot"

and "sudo gainroot
reboot"

With both keyboard open end closed and with stock kernel, kp48 & kp 49, i did this several time and trying different command but it always did reboot properly...

Sorry but i don't seems to be able to reproduce this issue...

Maybe if you use multiboot, you can try this:
http://talk.maemo.org/showthread.php?t=67866

i use this.

Oh god, please... Few posts ago Temporal clarified, what kind of reboot problem we're talking about (I admit, I should foresee, that most people won't read last page, and starting posting irrelevant sh|t, when asked about "reboot problem"), and we're still getting asnwers like "I got my device running for 235462365127654237 years, and I got no reboots"?

Please, read at least last 2-3 pages, before replying *facepalm*.

/Estel

Ps.

It's quite strange problem, cause - in my case - it appeared with kp48. Still, some people get it at much lower version, or haven't get it at all.

I wonder if it is really kernel related - still, I have no idea what may be causing this. I don't use any s0-called "miracle" speed/battery sh|t patches.

/Estel

I use same kernel as last time (kp49 from 2011-10-06) and i confirm that usb-networking problem still happens (it crashed my phone today during downloading files for updates over USB)
when I will upgrade to latest version of kp49 I will check again.

Add me to the ones, who would love to have this issue fixed. Or at least directed into some kind of "I know whats happening".
Struggling with this (reboot not reliable, whatever kind of command line is used), since installed KP months/years ago.
But hey, its just annoying, but not really a fatal error

It's not the same issue as the issue where the device won't finish booting or will enter into a (possibly temporary) reboot loop if you try to power it up with the charger plugged, is it?

My thought exactly - I at least have had both forms of the issue. But correlation and common cause are not guaranteed.

What I noticed was that in both cases the failure was not inevitable, though it did occur the majority of times.

Indeed. Reboot doesn't restart on either of my units, and nor will they get to the white dots 90% of the time with the charger plugged in (usually noticed after a crash.) Removing the charger enables the boot to succeed.