I am using Kubuntu Linux 12.10.  I installed the system on a Dell Latitude E6530 Laptop three days ago (Wed, 2 Jan 2012), and updated the system this morning.  When the system monitors blank out after a period of time, whether it be because I lock the screen using Ctrl-Alt-L, or whether the screen just times out, when I try to wake up the screen, the laptop monitor remains blank.  I do notice a "brightening" of the black screen, but nothing else happens.

At first, I thought it was strictly a "wakeup" problem, but now that I have a second (VGA) monitor plugged in, the bug remains, but *only* affects the laptop monitor.  Since at one point I was using ssh to transfer files from an older laptop to this one, I also know that the computer doesn't just "lock up" during this  time, but the screen just isn't working.  (Oh, heck, this is obvious:  I'm using the computer right now with a blank laptop screen.)  I can move program windows to the other screen,

At one point, I thought that I couldn't launch RandR, but what probably happens is that it opens on the laptop screen rather than the main screen--I like to have my Task Manager show only files on current screen and desktop--and I find if I clone my screen, the windows are pushed onto the monitor that works; thus, it seems that KDE still recognises the existence of the screen, even when the screen isn't displaying anything.

If I restart the computer, the laptop monitor will work normally again; and will usually go through several locks or "naps" before the problem comes back.  So far, it's happened at least two or three times a day.

Apparently, the Dell Latitude E6430 has been known to have problems with USB 3.0 ports (see http://brianmorristech.com/?p=953), so perhaps this might be the problem; I do not know how to disable USB 3.0, though, and plugging a mouse in the 2.x port (and later, a wireless mouse and keyboard dongle) doesn't seem to prevent the problem.  On the other hand, I also plug in the mouse's charger in one of the other 3.0 ports...  Having said that, keep in mind that the problem described in the link is a Windows issue as well, so it might not be applicable to Linux.

I also do not know how "sleep" and "hibernate" affect this bug.  I haven't been putting my laptop to sleep; I have only put the laptop in hibernation once, via "pm-hibernate", to test that it works.  (My swap is 33G, since I wanted to make sure there was plenty of room for the 16G of RAM I had, and I wasn't sure exactly how big the swap needed to be; perhaps that's another issue that ought to be addressed, but that's an installer thing...)

Reproducible: Sometimes

Steps to Reproduce:
1.  Install Kubuntu Linux with swap on a Dell Latitude E6530
2.  Lock the screen, and/or let the screen go blank on its own without locking it.
3.  Repeat #2 several times.  Eventually the monitor won't display anything, I think.
Actual Results:  
At some point, the laptop monitor will be black--maybe brighten a tiny bit--and won't display anything.

Expected Results:  
The unlock dialog should have popped up, or in the case of just blanking the screen, the original screen should have come up instead.

I chose "Major" because while under certain conditions the laptop is useful without the problem (I can use an external monitor, for example, and if I get a second, I probably won't notice it), it would be a pretty horrendous problem if I had to travel, and in the process of using my computer, I had to reset my computer on a regular basis, I'd be able to do some stuff, but it would be highly annoying.

I would add that this is almost a "Grave" problem.

Also.  I apologise for any horrendousness in my bug description.  I am a native English speaker, after all...